|
Leon County
Board of County Commissioners Agenda Item#16 June 10, 2025 |
| To: | Honorable Chairman and Members of the Board |
| From: | Vincent S. Long, County Administrator |
| Title: | Lake Munson Action Plan and Post-Drawdown Status Update |
| Review and Approval: | Vincent S. Long, County Administrator |
|
Department/Division Review and Approval: |
Ken Morris, Assistant County Administrator Nawfal Ezzagaghi, Assistant County Administrator Brent Pell, Director, Public Works Maggie Theriot, Director, Office of Resource Stewardship Charles Wu, Director, Engineering Services, Public Works |
|
Lead Staff/ Project Team: |
Anna Padilla, Stormwater Management Coordinator |
Statement of Issue:
This item provides a status update on the implementation and ongoing efforts related to the Lake Munson Action Plan, as approved by the Board at the October 11, 2022 meeting, and modified at the March 21, 2023 meeting. As directed by the Board at the April 9, 2024 meeting, this Action Plan update is provided one year after conclusion of the drawdown.
Fiscal Impact:
This item has no fiscal impact.
Staff Recommendation:
Option #1: Accept the Lake Munson Action Plan and Post-Drawdown status update.
Report and Discussion
Background:
This item provides a status update on the implementation and ongoing efforts related to the Lake Munson Action Plan (Action Plan), as approved by the Board at the October 11, 2022 meeting, and modified at the March 21, 2023 meeting (Attachment #1). The item outlines the key successes of the Action Plan and provides an update on the conclusion of the drawdown and refill of the lake. It provides detailed analysis of the water quality and stabilizing system during the drawdown and through the first year following lake refill, the progress of the invasive exotic vegetation management program, information on innovative technology exploration, a summary of the continued investment through two planned projects, and a summary of the next steps in the ongoing implementation of the Action Plan. As directed by the Board at the April 9, 2024 meeting, this Action Plan update is provided one year after conclusion of the drawdown.
This status report advances the following FY 2022 – FY 2026 Strategic Initiatives:
These particular Strategic Initiatives align with the Board’s Environment Strategic Priorities:
Lake Munson, located on the south side of Tallahassee, receives much of its flow from densely developed areas. Decades of development prior to environmental regulations, wastewater treatment facility effluent discharges into the system, and activities focused on flood reduction resulted in severe water quality and ecological problems.
Since the 1980s, local governments have invested over $291 million in ongoing efforts to restore Lake Munson and improve the water quality. More than 29 projects and 21 best management practices have been completed including infrastructure and restoration projects that provide water quality treatment, reduce sediment transport, and collect trash (Attachment #2). Leon County’s Lake Munson Restoration Project completed in the early 2000’s was a major effort with the primary goal of improving the water quality in Lake Munson. The project included the construction of the Lake Henrietta stormwater facility, improvements to Munson Slough with the creation of living shorelines to reduce erosion, removal of trash and the sediment delta from Lake Munson, and restoration of the wetlands around Lake Henrietta and Lake Munson.
Lake Munson is designated by state statute as a Class III waterbody, meaning it supports recreational use and fish consumption. While fish from Class III waters are generally considered safe to eat, the Florida Department of Environmental Protection (FDEP) and the Florida Department of Health may issue advisories for certain species, locations, or recommended consumption limits. To meet Class III standards and support a healthy ecosystem, a waterbody must meet specific biological, chemical, and physical criteria and maintain a balanced population of flora (aquatic plants) and fauna (fish, animals, and other aquatic organisms). In 2013, FDEP established a Total Maximum Daily Load (TMDL), for Lake Munson and Munson Slough (above Lake Munson), which includes additional waterbody-specific nutrient (i.e., nitrogen and phosphorus) concentration, biological, and physical property targets that must be met to support the designated uses of Lake Munson.
The water quality and ecological health entering Lake Munson have continued to noticeably improve with the significant investment in capital projects and restoration activities, resulting in a steady decline in nutrient concentrations (Attachment #3). The water quality in Munson Slough upstream of the lake has improved such that the nutrient concentrations remain below the TMDL target levels established by the State. Within Lake Munson, the nitrogen concentrations have been consistently below the State’s target and the phosphorus concentrations steadily declined to approach the State’s target. As part of the Leon County Water Quality Monitoring Program (Monitoring Program), water quality samples are collected quarterly in waterbodies throughout the county. Data collected through the program are reviewed by County staff and analyzed for trends. This information is summarized in the Annual Water Quality Report, which presents the previous year’s data. At the January 28, 2025 meeting, the Board accepted the 2024 Annual Water Quality Report which reflects the water quality sampling data collected through December 2023.
In Summer 2022, Lake Munson experienced a minor ecological setback despite measurable improvements in water quality. Extremely warm weather, combined with the lake’s shallow, stagnant conditions, created ideal circumstances for an algal bloom, rapid growth of invasive exotic aquatic vegetation, and a fish kill. These challenges presented an opportunity for immediate mitigation and evaluation of long-term strategies for managing Lake Munson. From this, the Action Plan was developed, guided by industry best practices and shaped by input from State agency partners, contracted environmental and engineering experts, and local stakeholders. This plan takes a comprehensive approach, not only targeting water quality but also aiming to build a more diverse and resilient ecosystem with balanced plant and animal life.
Approved by the Board on October 11, 2022, the Action Plan includes short- and long-term strategies for the restoration and ecological improvement of Lake Munson and articulates the decades of investment in upstream infrastructure projects, improving the water quality and ecological health of the lake. The Action Plan takes a holistic approach through a drawdown coupled with enhanced monitoring of the lake’s response during and after the drawdown, while also providing long-term strategies to supplement the State’s in-lake vegetation management activities and deliver a higher level of service to County residents (Attachment #1). Updates to the Board throughout the drawdown, and in the two years following, highlight the Action Plan implementation, provide information on the lake’s recovery, and present new data and information.
The drawdown, a key component of the Action Plan, began in November 2022 to quickly mitigate the rapid growth of hydrilla and algal blooms and as a sediment management strategy. Drawdowns are a natural process that allow nutrient-rich sediments to de-water, compact, oxidize, and form a hardened crust over the lake bottom. This hardened crust serves to “cap” the underlying sediment which provides habitat for fish spawning and reduces nutrient recycling into the water once the lake is refilled. At the March 21, 2023 meeting, the Board approved modifications to the Action Plan, which included extending the drawdown through the Spring of 2024 to allow additional time for the lake bottom sediments to dry out. The extended drawdown was a result of coordination with the Florida Fish and Wildlife Conservation Commission (FWC) and higher than anticipated rainfall during the 2021-2022 winter months.
With the extension of the drawdown through the rainy season, an Emergency Action Plan was developed to close the Lake Munson dam in anticipation of flooding or significant rainfall events to protect downstream properties from flooding and allow the sediment in the lake to settle prior to discharge. On two occasions the Emergency Action Plan was implemented, and the drawdown was suspended. First in early September 2023, in advance of Hurricane Idalia, and a second time in December 2023, following heavy rainfall and subsequent high downstream water levels. During both drawdown suspensions, staff coordinated with FWC and monitored downstream conditions and the water quality at Lake Munson. When the water in Lake Munson was not turbid (appeared clear), and downstream water levels were low with ample storage capacity, the drawdown resumed.
The Action Plan includes Enhanced Monitoring which provides information on the lake’s response to the drawdown and implementation of the lake management strategies in the years following. In conjunction with the drawdown extension, the Board approved a Drawdown Water Quality Study. This study included monthly water chemistry sampling in Munson Slough upstream and downstream of the lake, offering valuable data on the system’s stability throughout the drawdown. In addition, quarterly Aerial Lake Bottom Topographic Surveys were conducted to measure sediment compaction through the drawdown. Following conclusion of the drawdown, the Post-Drawdown Water Quality Study began to monitor the lake’s response through monthly water chemistry sampling and flow data collection of the water entering and leaving Lake Munson.
The long-term strategies of the Action Plan focus on proactive management of the lake vegetation and sediment, which began with the lake refill. An invasive exotic vegetation management program supplements the State’s program and provides more frequent treatments over smaller areas, impacting the system less. These treatments are coupled with an algal bloom management program to mitigate any naturally occurring blooms on Lake Munson. Through ongoing innovative technology exploration, new and innovative ideas and scientific data are being explored for new opportunities and strategies that could benefit Lake Munson. As these opportunities arise, they will be presented to the Leon County Science Advisory Committee (SAC) and State-agency partners, with viable solutions brought to the Board.
Looking to the future, routine periodic drawdowns every five to 10 years will be utilized for sediment management, continuing to improve the water quality in Lake Munson. Engagement with various entities is key in the Action Plan. Coordination with State-agency partners will continue, evaluating the progress of the drawdown. Quarterly updates on the progress of the drawdown and the data collected through the enhanced monitoring will continue to be presented to the SAC for review and evaluation. And finally, based on previous Board direction, the next status update will be provided to the Board in June 2026, at the conclusion of the Post-Drawdown Water Quality Study.
As detailed in the Analysis section, this item provides a status update on the implementation of, and ongoing efforts related to, the Action Plan. In addition, this item provides an update on activities and progress since the previous update in April 2024. More information on the implementation of the Action Plan since adoption can be found on the dedicated Lake Munson website at www.LeonCountyWater.org/LakeMunson.
Analysis:
This status update highlights the key accomplishments of the Action Plan, summarizes progress on its implementation, and outlines next steps for the coming year and beyond. Since the previous update to the Board in April 2024, the drawdown concluded, and the lake refilled. Enhanced monitoring transitioned to the Post-Drawdown Water Quality Study, the invasive exotic vegetation management program continued, innovative technologies were explored, and engagement with the SAC and citizen stakeholders was ongoing. These and other strategies implemented through the Board approved Action Plan have given rise to numerous notable and significant achievements in the continued improvement of Lake Munson.
Lake Munson Key Achievements and Successes
Implementation of the Action Plan has been paramount in the restoration and protection of Lake Munson now and into the future. The Action Plan employs a holistic approach to lake management aimed at improving and protecting the entire ecosystem with continued water quality improvements, supporting a native and diverse system, and meeting the State’s requirements for water quality and well-balanced flora and fauna. Since adoption of the Action Plan by the Board in October 2022, Leon County staff, in coordination with State-agency partners, have continuously monitored Lake Munson and evaluated the progress against ecological targets and State requirements. Notable findings and achievements stemming from the Action Plan include:
Improving water quality both within Lake Munson and its outflow is the foundation of the Action Plan. The strategies included in the Action Plan are aimed at providing benefit, and restoring and protecting the ecosystem, while minimizing potential harm. The data collected through the County’s Monitoring Program, coupled with the Action Plan Enhanced Monitoring, tracks the lake’s response to the drawdown and long-term management strategies. Comparing this data to historical water quality data provides insight into the overall impact of the Action Plan. Overall, this comparison indicates the drawdown provided water quality benefits.
In Lake Munson following the drawdown, nitrogen concentrations remain better than the TMDL and are lower than the 2022 average nitrogen concentrations in the lake (Attachment #4). The phosphorus concentrations in the lake also dropped below the 2022 average phosphorus concentration and continue to decrease.
The water quality in Munson Slough downstream of the lake has predominantly been better than State standards leading up to, during, and following the drawdown and has continued to improve (Attachment #5). Munson Slough downstream of the lake does not have a TMDL for nutrients, so the State uses Numeric Nutrient Criteria (NNC) as one method of determining if a waterbody meets nutrient water quality standards; in addition, the nutrient TMDL for Munson Slough (above Lake Munson) is often used for comparative purposes because it is more restrictive. The nutrient concentrations in Munson Slough downstream of the lake are largely below both the NNC for Munson Slough and the TMDL for Munson Slough (above Lake Munson) and remain consistent with the water quality concentrations during the five‑year period of improved water quality leading up to the drawdown.
The restoration of Lake Munson is evident by the abundant wildlife in and around the lake. Recently, the lake is a popular destination for birders who can watch numerous bird species at any given time, including osprey and limpkins. Most notably is the recent sighting of Everglade snail kites, a federally endangered species. These unique bird feeds almost exclusively on apple snails. Their appearance at Lake Munson is important because these birds have historically been limited to central and south Florida. County staff are working closely with FWC to monitor and protect the Everglades snail kites. Beyond birding, the lake is also used for fishing, hunting, and boating.
The success of the Action Plan is a product of the holistic approach to lake management and the implementation of proven, beneficial strategies and best practices. Through the Action Plan, County staff provide quarterly updates to the SAC including water quality results and overall progress. At the May quarterly update, the SAC consensus was the drawdown effectively trapped nutrients in the sediment as intended and the long-term strategies outlined in the Action Plan remain the preferred approach for lake management and achieving the State’s requirements.
Drawdown Conclusion and Lake Refill
The drawdown, which began in November 2022, officially concluded on May 17, 2024, and the process of refilling the lake began. Based on FWC’s recommendation, the gates on the dam were incrementally closed to allow the water levels in the lake to slowly rise. Throughout the refill, the County coordinated with FWC and monitored water levels and conditions in the lake and downstream, as well as potential significant rainfall events.
The slow refill process proved beneficial and prevented a shock to the ecosystem. By gradually raising the water level, the aquatic vegetation in the lake had the opportunity to adapt to the new and changing conditions, and what did not adapt slowly died off. This slow and methodical refill prevented a total plant kill and subsequent algal bloom. The slow refill of the lake, in conjunction with the invasive exotic aquatic vegetation management, allowed the native species in the seed bank to begin their reestablishment in the lake.
As the lake began to refill, FWC planned to restock fish in Lake Munson. Although originally scheduled for fall 2024, the effort was postponed due to low water levels which prevent the safe release of fish and access to the open waters of the lake. County staff are continuing to coordinate with FWC to reschedule the restocking.
Overall, the drawdown was effective in addressing the ecological challenges observed during the summer of 2022, including rapid growth of invasive exotic species and algal blooms. The process achieved key objectives such as allowing lake bottom sediments to dry, compact, and form a “cap” that helps reduce nutrient recycling. The gradual refill supported the reestablishment of native vegetation. Data collected through the Enhanced Monitoring component of the Action Plan indicate continued system stabilization and sediment compaction.
Enhanced Monitoring
The Action Plan includes enhanced monitoring centered around data collection and analysis, focusing on the overall health of the lake during the drawdown and in the two years after the lake is refilled. During the drawdown, water quality samples collected in Munson Slough through the Drawdown Water Quality Study expanded on the County’s Monitoring Program and provided information on the stability and response of the system to the drawdown, while aerial lake bottom topographic surveys indicate the amount of sediment compaction. During the two years following the drawdown, water quality data collection and analysis in the Post-Drawdown Water Quality Study tracks the reaction and progression of the system as long-term lake management strategies are implemented.
A healthy ecosystem depends on more than just good water quality, it also requires a diverse and balanced mix of plant and animal life. Leon County takes a comprehensive approach to assessing its waterbodies, evaluating their biological, chemical, and physical conditions together. This includes looking at water quality in the context of the surrounding plants, animals, and other organisms. While the enhanced monitoring water quality data provides valuable insight into system stability and how it responds to change, it should not be the only measure of health. Water chemistry can be affected by external factors like weather (i.e., temperature, rainfall), water levels, upstream inflow, dam discharges, and invasive exotic species treatments. A broader perspective is essential when evaluating the overall health of the system.
Drawdown Water Quality Study
With the extension of the drawdown at the March 21, 2023 meeting, the Board approved the addition of a Drawdown Water Quality Study to the Action Plan. This study supplemented the County’s quarterly water chemistry sampling to attain monthly water quality data in Munson Slough both upstream and downstream of the lake, until the drawdown concluded. The samples collected during the drawdown provide information on the water chemistry concentrations entering and leaving the lake and insight into how the lake reacted during the drawdown.
Water quality samples were collected from March 2023 through May 2024. The sample results were analyzed alongside lake stages and other external factors to identify trends (Attachment #6). Throughout the drawdown, the water quality in Munson Slough remained at or better than the TMDL target for Munson Slough (above Lake Munson). As the drawdown progressed, the lake continued to stabilize and nutrient concentrations in the water leaving the lake generally trended lower. Elevated nutrient concentrations were observed in March and September 2023, and again in April and May 2024, due to system instability and external influences.
System instability can result from fluctuations in water levels or changes in lakebed vegetation, both of which affect water quality as it moves through the lake. In March 2023, water quality samples were collected following several weeks during which the lake was predominantly drained. These conditions contributed to higher nutrient concentrations leaving the lake than entering it, indicating an unstable system. Although the exact cause of the instability and higher concentrations is unknown, supporting water chemistry data—such as increased levels of nutrients and suspended materials—suggests that a shallow, isolated pool may have drained into the flow-through channel. At the time, the lake bottom had noticeably less vegetation, which made it more vulnerable to disruption from fluctuating water levels, weather events, or wildlife—such as an alligator moving through the area. In these conditions, isolated pools of stagnant, nutrient-rich water had formed. If disturbed, wildlife activity could have physically linked these pools, causing the nutrient-laden water to mix and flow more freely across the lakebed.
The elevated nutrient concentrations leaving the lake in September 2023 were attributed to a syphon effect that occurred as the remaining water drained from the lake when the drawdown resumed following the temporary suspension due to Hurricane Idalia. The syphon effect pulled very fine, loose sediment from the flow-through channel in the lake into the water column, resulting in a temporary nutrient spike. This also explains why phosphorus concentrations were higher than nitrogen—because phosphorus binds more readily to sediment, which was being pulled into the water column during the siphon effect.
Elevated nutrient concentrations in April and May 2024 were attributed to prior invasive exotic vegetation treatments in Lake Henrietta, Munson Slough upstream of the lake, and the flow‑through channel in the lake. Increased nutrient concentrations can occur following invasive exotic vegetation treatments because nutrients can release into the water column when the invasive exotic vegetation dies off. The concentrations remained around the TMDL for Munson Slough (above Lake Munson) and, although the concentrations were higher than previous months, the increase is not an indication of drawdown effectiveness. To achieve the State’s standard of a balance of flora and fauna, invasive exotic vegetation treatments are necessary and the overall benefit to the system outweighs the minimal short-term changes in water chemistry.
Overall, the Drawdown Water Quality Study sample results indicate that through the drawdown, the lake bottom sediments consolidated, and the system grew more stable. The decades of significant investment in upstream improvements in the Lake Munson drainage basin improved the water quality entering Lake Munson, which has not changed with the drawdown. Throughout the drawdown the nitrogen and phosphorus concentrations in Munson Slough have primarily been better than or just above the State TMDL.
Aerial Lake Bottom Topographic Survey
Aerial topographic surveys provide data on the elevation of the lake bottom and can be used to estimate the amount of sediment compaction over the course of the drawdown. The original Action Plan included a survey at the beginning of the drawdown after the lake bottom was exposed and again before the lake was refilled. With the extension of the drawdown in March 2023, quarterly aerial surveys throughout the drawdown were added to the Action Plan.
The first aerial survey was flown at the beginning of the drawdown in November 2022, followed by quarterly surveys in April, August, and October 2023. Additional surveys were planned for January and April 2024; however, these final two surveys could not be flown due to high water levels in the lake beginning in December 2023, which resulted in most of the lake bottom submerged through the end of the drawdown in Spring 2024.
The aerial topographic survey data shows clear signs of sediment compaction, with the most significant improvements occurring around the lake’s edges, areas that were exposed more frequently during the drawdown. Although a final survey was not conducted and no direct comparison to pre-drawdown conditions can be made, the data obtained suggests the drawdown was effective in promoting sediment consolidation.
Post-Drawdown Water Quality Study
As discussed in previous Lake Munson status reports, once the lake refills it can take several years for the nutrient levels and the ecosystem to stabilize following the continual state of transition and flux associated with a drawdown. The Post‑Drawdown Water Quality Study collects monthly water quality and flow data during these two years after the drawdown at four locations: two upstream of Lake Henrietta, one upstream of Lake Munson, and one downstream of the lake. The study provides an excellent opportunity to monitor and quantify the effects of the drawdown and the water quality in Lake Munson.
In June 2024, the Post-Drawdown Water Quality Study began, and sample results through April 2025 were compiled and evaluated for trends (Attachment #6). Overall, the water quality remains around the State’s TMDL limits for Munson Slough (above Lake Munson) and the lake continues to stabilize. So far, the water quality following the drawdown is as anticipated, with observed nutrient variability attributed to external factors such as invasive exotic management and fluctuations in flow.
Since the lake refill, nutrient concentration variability can be attributed to a mix of factors. One major contributor was the invasive exotic vegetation treatments that began in July 2024 on Lake Munson, Munson Slough upstream of the lake, and Lake Henrietta. These treatments began in July 2024 and were applied monthly until October, then increased to every other week until they were paused in December for the winter. As the treated vegetation died off, it released nutrients back into the water, contributing to the rises and dips observed in the data.
Flow conditions in Munson Slough also played a role in nutrient concentration variability. As storms and low-flow periods do cause erosion or carry varying nutrient loads from upstream, adding to the fluctuations. The shift from the County’s routine quarterly sampling to monthly sampling with the enhanced monitoring made these changes more visible. Given all these variables, water quality is best understood by looking at overall trends rather than focusing on individual sample results.
Overall, since the drawdown, the water quality remains around the TMDL for Munson Slough (above Lake Munson), the lake continues to stabilize and improve, and nutrient concentrations point to a downward trend. The results of the Post-Drawdown Water Quality Study will continue to be evaluated through the second and final year of enhanced monitoring to track the lake’s ongoing response to the drawdown and the implementation of the long-term lake management strategies.
Long-Term Best Management Practices
As a State-managed waterbody, the County relies on State agencies for lake management such as aquatic vegetation treatment and lake restoration projects. However, the Action Plan outlines an expanded role for the County, supporting and enhancing the State’s lake management efforts and responsibilities. It also includes continued coordination with State agencies to pursue long-term restoration opportunities.
The long-term strategies in the Action Plan focus on proactive vegetation management to support a more native and diverse ecosystem in Lake Munson. To supplement the State’s efforts, the County has established an Invasive Exotic Vegetation Management Program that provides faster response times and targeted treatments, minimizing disruption to the system. In addition, the Algal Bloom Management Program addresses naturally occurring blooms by treating them as they appear, helping to reduce their impact on nearby residents. The County uses a single contractor for both invasive exotic aquatic vegetation and algal bloom treatments, ensuring a more efficient response and reducing the risk of overtreatment. The Action Plan also includes exploration of new technologies and scientific data for potential opportunities and strategies that could benefit Lake Munson.
Invasive Exotic Vegetation Management Program
One of the County’s goals for Lake Munson is a balanced, diverse, and native plant community. Diverse native species create a healthier ecosystem, serving as food and nesting habitat for fish and wildlife, and build resilience and biodiversity. Invasive exotic vegetation can adversely impact native plant communities and, if left untreated, will rapidly colonize and take over a waterbody. While invasive exotic species can never truly be eradicated, vegetation treatment can control the invasive exotic species, which allows for and promotes the growth of native vegetation.
The County’s Invasive Exotic Vegetation Management Program implemented through the Action Plan has been effective in controlling the invasive exotic species in Lake Munson and promoting native vegetation growth. In consultation with FWC, treatments were conducted by the County through a Continuing Service Contractor in Spring of 2024 prior to the conclusion of the drawdown, followed by a coordinated effort of treatments by the County and FWC over the Summer and Fall of 2024 and resuming in the Spring of 2025.
The drawdown was successful at mitigating the rapid growth of hydrilla in Lake Munson by drying out the plants and the underground tubers which help the plants spread. Since the drawdown, the invasive exotic vegetation treatments have controlled the spread of hydrilla from upstream, as evident by the limited amounts of hydrilla observed in the lake since the drawdown. Unlike a seed bank which can survive a drawdown, tubers lose viability when dried out, limiting regrowth when the lake is refilled. In addition to spread by tubers, hydrilla can also spread by fragmentation, or when a small piece breaks off and establishes in another area. To prevent the reestablishment of hydrilla due to fragmentation, prior to the drawdown conclusion, the Invasive Exotic Vegetation Management Program began treating the flow‑through channel in the dry Lake Munson lake bottom and areas upstream, including Munson Slough and Lake Henrietta. Three treatments were performed, beginning in March 2024 and continuing through the end of April 2024.
The drawdown was also beneficial in reducing the potential growth of water hyacinth, a fast‑growing aquatic plant that forms floating mats on the water surface. During the winter of 2024-2025, Lake Munson went through a three-month period in which the lake predominantly held water. While this period did not allow the sediment to dry out as planned, the lake’s response during this period had positive and unexpected results. As presented in the April 9, 2024 agenda item, this period of higher water levels allowed the water hyacinth seeds in the sediment to germinate (grow), and with the subsequent draining of the lake the plants died off before they were able to seed. This natural filling and draining of the lake used up part of the seed bank, thereby reducing future growth.
Since the conclusion of the drawdown, the predominant invasive exotic species has been water hyacinth. Through invasive exotic vegetation treatments in Lake Munson, and upstream in Munson Slough and Lake Henrietta, the spread of water hyacinth has been controlled. The goal of the Invasive Exotic Vegetation Management Program is to treat smaller areas more frequently, which reduces the shock on the system. In July 2024, the County’s contractor began treatments of approximately 32 acres each month. While these applications effectively limited the spread of water hyacinth, more frequent treatments were needed to combat the aggressive growth cycle and reduce the amount of water hyacinth.
Beginning in early October 2024, FWC augmented the County’s efforts with additional monthly treatments on Lake Munson. FWC's treatments specifically targeted vegetation that had not responded to the County’s applications approximately two weeks prior. The alternating treatments continued every two weeks through late November 2024 and proved effective at controlling and reducing the water hyacinth, as each application only needed to cover a smaller area, with hyacinth cover steadily shrinking. During subsequent treatments in late October and November 2024, the County’s contractor treated 24 and 20 acres, respectively. Prior to the planned treatment in early December, Tallahassee experienced two nights of frost followed by several days of low temperatures, which damaged the remaining water hyacinth and acted as a natural control method. Water hyacinth does not tolerate cold weather and with the onset of winter, the invasive exotic treatments were suspended until spring.
Invasive exotic vegetation treatment on Lake Munson, Munson Slough, and Lake Henrietta resumed in March 2025. The County’s initial application in March treated approximately 34 acres followed by approximately 30 acres in April. In a coordinated effort between Leon County and FWC, the intent is to conduct treatments approximately every two weeks to continue reducing the coverage of the invasive exotic species and promote native vegetation growth. Treatments will continue through the Summer and Fall until the weather cools again next Winter.
The success of invasive exotic vegetation control is evident in the decreasing size of areas requiring treatment over the course of a vegetation control season. During each visit, treatments have targeted relatively small acreages while still addressing most of the invasive exotic vegetation present. This consistent reduction in treatment area highlights the effectiveness of the program and represents the declining presence of invasive aquatic vegetation in the lake.
Despite the increasingly smaller amounts of water hyacinth, the effectiveness of the treatments is not evident from the eastern shore of the lake. Because of the floating nature of the vegetation and the characteristics of the lake, mats of water hyacinth have been present at the boat ramp and the dam outfall channel since the conclusion of the drawdown. Unlike hydrilla that attach to the lake bottom through roots, water hyacinth is free floating on the water surface and can be pushed around the lake by the wind or current. The wind patterns are predominantly from west to east, flowing through the lake from the northwest to the southeast, which result in the continual transport of the water hyacinth to the eastern shore and the dam. Although water hyacinth can grow from the seed bank, the bigger challenge on the east side of the lake is the transport of water hyacinth to this location.
Lake Munson has approximately 250 acres of open water due to the drawdown’s hydrilla mitigation and the water hyacinth control through the Invasive Exotic Vegetation Management Program. At this time, vegetation treatment remains the most viable option, and water hyacinth control and reduction on the eastern shore and at the lake outfall remains the primary focus in the year ahead.
In the meantime, to restore boater access to this open water at Lake Munson, FWC, in coordination with Leon County Parks and Recreation, conducted boat landing maintenance and cleared overgrown floating vegetation, primarily water hyacinth, near the Gill Waters Preserve landing. The work, completed in mid-May 2025, followed an environmental review by an FWC wildlife biologist to ensure minimal ecological disruption. As a result, access to open water has been successfully reestablished for boaters, kayakers, and other lake users to enjoy this valued community resource.
Algal Bloom Management Program
An Algal Bloom Management Program was included in the Action Plan at the request of area residents to mitigate the naturally occurring blooms on Lake Munson by treating them when they occur, providing relief to area residents affected by the blooms. Neither the County nor State agencies have historically treated algal blooms on Lake Munson.
No algal blooms on Lake Munson were reported to FDEP or observed by County staff since the summer of 2022. Algal bloom management is a reactive program in that blooms are treated after they occur. Because no blooms have been reported, there have yet to be any treatments through this program. The County’s contactor is prepared to quickly respond should any blooms be reported or observed.
Innovative Technology Exploration
Strategies for lake management continue to evolve as new information becomes available and technologies develop. County staff are continually evaluating data, science, and strategies for best practices and emerging opportunities that have the potential to achieve the goal of water quality and ecological improvements, providing the most benefit with minimal negative impacts. As these opportunities arise, they will be presented to the SAC and State-agency partners, with viable solutions incorporated into the County’s efforts or brought to the Board for further consideration.
Innovative techniques and potential strategies for lake management have been identified through ongoing partnerships with State-agencies, citizen stakeholders, and other environmental champions. Over the past year, staff have engaged in conversations with the County’s Environmental Consultant, explored products for in-lake mitigation, and met with university researchers to discuss various methods and ideas. These strategies include sediment inactivation products to prevent nutrients from being released into the water column, and a pilot project that utilizes plants developed to remove phosphorus.
Conclusions have yet to be made and the evaluation of these, and any new ideas or technologies, continue. At this time, the Board approved Action Plan remains the preferred strategy in achieving the goal of a healthy ecosystem with water quality meeting the State standards and a well-balanced and diverse community of flora and fauna.
Continued Investment Through Planned Projects and Maintenance
The effort to restore Lake Munson goes beyond the Action Plan, with capital improvement projects for Lake Henrietta and Munson Slough planned to begin later this year.
Lake Henrietta Sediment Removal Project
Lake Henrietta is a constructed regional stormwater management facility that slows the rate of stormwater flowing to Lake Munson and provides a place to collect nutrient-rich sediment and floating debris before it can enter Lake Munson. Since construction in the early 2000s, the stormwater management facility has captured over 53,000 cubic yards of sediment and debris. Leon County was awarded a grant by the U.S. Environmental Protection Agency (EPA) for the Lake Henrietta Sediment Removal Project. County staff have been working with EPA to complete the required environmental review process and grant agreement development. The design of the project is anticipated to commence this Summer with construction to follow in FY 2026. This $2 million project will remove the material accumulated in Lake Henrietta to enhance the facility’s performance, reduce sediment flowing downstream to Lake Munson, and improve the water quality of the Lake.
Munson Slough Embankment Repair Project
The Munson Slough Embankment Repair Project is a $1.6 million initiative to stabilize eroded sections upstream of Lake Munson and safeguard long-term water quality. The County has committed $400,000 from its Stormwater Infrastructure Preventative Maintenance Program and is actively seeking additional funding. In May 2024, the Board approved a $1.2 million grant application through Florida’s Hazard Mitigation Grant Program. The application was submitted in June, and the County is currently awaiting the outcome.
This project builds on the County’s Lake Munson Restoration Project from the early 2000s, which used living shorelines to reduce erosion, cut sedimentation, improve water quality, and enhance wildlife habitat. While that effort delivered strong results, some upstream areas have since experienced renewed erosion. The new embankment repairs will restore and reinforce these gains—stabilizing banks, replanting native vegetation, and reducing sediment flow into Lake Munson to protect the health of the ecosystem for years to come.
Next Steps
In the year ahead, the enhanced monitoring, Long-Term Best Management Practices, and Innovative Technology Exploration will continue to further the Lake Munson restoration progress which will be evaluated against ecological targets. The Post-Drawdown Water Quality Study will collect monthly water quality and flow data in Munson Slough and County staff will continue to monitor the water quality and stabilization of the lake. The invasive exotic vegetation treatments will continue monthly until the winter when they will be suspended and will focus on the eastern side of the lake and the outfall channel to the dam. The County treatments will be conducted in coordination with, and augmented by, FWC as necessary. The lake will be monitored for potential algal blooms and should any be reported to FDEP or observed by County staff, the blooms will be promptly treated.
County staff will continue to evaluate the information collected through the enhanced monitoring program which will be presented to the SAC in quarterly updates. Coordination on the progress of the drawdown with State-agency partners and engagement with citizen stakeholders also will remain ongoing. And finally, staff will provide an update to the Board on the progress of Lake Munson in June 2026, at the conclusion of the two-year Post-Drawdown Study.
Conclusion
This update summarizes progress on the Lake Munson Action Plan, one year after the lake’s drawdown concluded. Since the 1980s, over $291 million has been invested in restoring the lake and its watershed through infrastructure improvements and best management practices. These efforts have led to measurable water quality improvements in both Lake Munson and Munson Slough, with nutrient levels now meeting or trending toward State targets. In addition, an abundance of wildlife can be found in and around the lake including fish and numerous bird species. The drawdown effectively mitigated the ecological issues which occurred in Summer 2022, such as algal blooms, invasive exotic vegetation, and a fish kill, allowing sediments to compact and native vegetation to reestablish.
The Action Plan continues to guide restoration through enhanced monitoring, capital projects, vegetation management, and the exploration of innovative technologies. The County’s contractor is actively managing invasive exotic plants like water hyacinth and remains prepared to respond to any algal blooms. Monitoring data is regularly reviewed and shared with the SAC, while coordination with State agencies and community stakeholders remains ongoing. The Post-Drawdown Water Quality Study and related activities will continue through the coming year, with the next update to the Board scheduled for June 2026.
Options:
Recommendation:
Option #1
Attachments: