Water bodies, watersheds and storm water
Lake Apopka
Once a world-class bass fishery, years of abuse has caused Lake Apopka to be tagged with the infamous title of Florida’s most polluted large lake. Restoring Lake Apopka’s water quality and ecosystem health is paramount to the St. Johns River Water Management District’s overall Lake Apopka Basin program.
In response to the District’s efforts, water quality has improved for more than a decade. Since 1992, phosphorus levels in the lake have decreased 41 percent, and water clarity is 34 percent better than earlier conditions.
Located in northwest Orange and southeast Lake counties, Lake Apopka is the headwaters of the Ocklawaha Chain of Lakes.
Fed by a natural spring, rainfall and stormwater runoff, water from Lake Apopka flows through the Apopka-Beauclair Canal and into lakes Beauclair and Dora. From Lake Dora, water flows into Lake Eustis, then into Lake Griffin and then northward into the Ocklawaha River, which flows into the St. Johns River.
The lake’s decline
Lake Apopka suffered a century of abuse beginning in the 1890s when construction of the Apopka-Beauclair Canal lowered lake levels by a third.
The decline of Lake Apopka can be traced to:
- The loss of 20,000 acres of wetlands along the lake’s north shore to farming operations beginning in the 1940s
- Agricultural discharges laden with phosphorus until the late 1990s
- Treated wastewater discharges from shoreline communities prior to the 1980s
- Discharges from citrus processing plants prior to the 1980s
The increase in nutrients discharged into the lake led to a chronic algal bloom, and Lake Apopka’s waters turned pea green. The cloudy water prevented sunlight from reaching underwater vegetation critical to fish and wildlife habitat.
The continual settling of dead algae created a thick layer of soupy muck, which also destroyed the habitat necessary for fish and wildlife to thrive. The bass population significantly declined as gizzard shad became the predominant fish species in the lake. Once the bass disappeared, all the fish camps closed.
Downstream to the north, the pollution spread throughout the Ocklawaha Chain of Lakes. To protect the Ocklawaha Chain, the flow of pollutants from Lake Apopka had to be stemmed.
The Lake Apopka Marsh Flow-Way treats water from the lake in wetland cells, releasing cleaner water back to the lake.
The restoration of Lake Apopka
The Lake Apopka Restoration Act of 1985 and Florida’s Surface Water Improvement and Management (SWIM) Act in 1987 paved the way for restoration work to begin. A SWIM plan outlines restoration activities.
The primary goals for the restoration of the lake’s ecosystem are to:
- Reduce the amount of phosphorus going into Lake Apopka
- Remove phosphorus and other suspended sediments from the lake (by filtration through the Marsh Flow-Way and by mass removal of gizzard shad)
- Improve the food-web structure by removing gizzard shad
- Restore habitat through restoration of the shoreline (known as the littoral zone), increased fluctuation in lake levels and restoration of the north shore farmlands to wetlands
Reducing the amount of phosphorus entering the lake
- North Shore Restoration Area (NSRA)
More than 85 percent of the phosphorus going into Lake Apopka was from farms on the lake’s north shore. To combat this problem, the District and the U.S. Department of Agriculture (USDA) purchased almost all of the farms for restoration over the past decades, reducing discharges of excessive nutrients from those sites.
Purchase of the farms has removed the NSRA from agricultural production and restored the area to a more natural condition.
Restoration of wetlands on the NSRA reduces stormwater discharges to Lake Apopka and related nutrient loading, accelerating the restoration of the lake. The restoration and remediation plan focuses on the infrastructure requirements and soil inversion work needed in the NSRA to prepare the system for reflooding and wetland restoration. The “soil amendment” acts like a magnet, trapping excess phosphorus as it leaves the soil, before it enters the water column. Soil inversion was completed in May 2009, reducing contaminants to safe levels on nearly 4,000 acres of the NSRA.
As the necessary infrastructure construction is completed for each phase, a biological assessment will be prepared for review and submission to the U.S. Fish and Wildlife Service (USFWS). With USFWS concurrence, saturation and restoration flooding may begin.
This infrastructure is designed to help establish full wetland habitat with a fairly wide range of water levels. The infrastructure will function to release water from the fields during rainy periods when desirable water levels are exceeded.
A tractor pulls a special plow that places potentially contaminated soil deep below the surface as part of a soil inversion project.
As the infrastructure work and soil preparation are completed in phases and USFWS has given approval, an area can then be saturated to begin the restoration part of the project. During this saturation period, monitoring of soil pesticide concentrations will be ongoing to ensure that pesticide levels are below the target levels.
Once the fields have been saturated and wetland plant coverage is sufficient, additional water can be added to an area. The current strategy for habitat restoration on these fields will be a variety of emergent marsh habitat for an extended period. Increase in water levels and reconnection of areas of the NSRA to Lake Apopka could occur first after contaminant levels in fish have been shown not to present a risk to bird health.
- The Marsh Flow-Way
The Marsh Flow-Way, which is a constructed wetland, is located along the northwest shore of Lake Apopka and west of the Apopka-Beauclair Canal.
The system covers approximately 760 acres and contains four individual wetland cells, in addition to levees, canals and ditches. The Marsh Flow-Way treats water pumped into it from Lake Apopka. The lake’s water has excessive amounts of phosphorus, algae and suspended matter. Water flows west to east and is controlled by screw gates and riser boards in the individual cells. Treated water from all cells collects in a pump basin, where water is pumped into the Apopka Beauclair Canal. Most of the cleaner, treated water returns to Lake Apopka, while the remainder flows downstream toward Lake County’s nutrient removal facility (NuRF).
Dominant vegetation communities growing in flow-way cells are shallow marsh and shrub swamp. Shallow marsh includes species such as pickerelweed (Pontederia cordata), arrowhead (Sagittaria lancifolia), cattail (Typha spp.), while shrub swamp includes primrose willow (Ludwigia peruviana), and some Salix spp. Open water areas are also common in wetland cells.
As incoming lake water passes through the Marsh Flow-Way’s emergent vegetation, the water’s flow rate slows and suspended particles, which contain phosphorus and other nutrients, settle out of the water column. The accumulating settled organic particles, along with settled decayed wetland vegetation, form new organic material layers, which overlay native soils. Retention time of lake water within the flow-way system typically ranges between two and seven days in the individual wetland cells. Water depths in the system can vary between 12 and 24 inches.
- Harvesting gizzard shad
Removing gizzard shad from the lake removes the phosphorus contained in the shad’s bodies as well as reduces the internal recycling of phosphorus within the lake. This improves water clarity by reducing the number of algae, which depend upon phosphorus for growth.
Harvesting shad from other lakes has resulted in an improved food web, reduced algae, improved water clarity and improved conditions for game fish populations. This procedure may produce the same results in Lake Apopka.
Restoring aquatic habitat
The District has planted wetland plant species behind protective barriers in Lake Apopka to provide habitat for fish and wildlife. These planting efforts are becoming less necessary as the lake’s water quality and clarity improve and native aquatic plants reestablish themselves.
An ongoing effort is under way to map the locations and extent of more than 350 native submersed plant beds. Improved water clarity has also made it possible for the nonnative invasive plant hydrilla to grow in the lake. Hydrilla can quickly outcompete native plants, so staff efforts are focused on locating and treating these undesirable plants with herbicides.
Challenges
Restoring Florida’s most polluted large lake has come with unforeseen problems. An estimated 676 birds died on former farms at Lake Apopka during late 1998 and early 1999. Most were American white pelicans, wood storks and great blue herons. Organochlorine pesticide (OCP) residues remaining from agricultural practices were primary causative factors in, or the cause of, the death of many of these birds. Birds accumulated OCPs by consuming contaminated fish. The District has conducted research to better understand the accumulation of OCPs through the food chain, from contaminated soil to fish, and from fish to fish-eating birds. The knowledge generated guides restoration of the former farmlands at Lake Apopka and is also applicable to other projects designed to restore ecosystems impacted by agriculture.
Accomplishments
Eelgrass beds are reocurring in Lake Apopka as water conditions improve.
The District’s Governing Board approved a rule in 2002 limiting the amount of phosphorus that can be discharged into Lake Apopka or its tributaries as a result of new construction in the lake’s watershed. The District has partnered with local, state and federal agencies to:
- Purchase more than 19,000 acres of agricultural land along the lake’s north shore, reducing the discharge of phosphorus from the farms and providing an opportunity to restore the former marshes to wetlands. About 5,000 acres have been restored to wetlands, with a goal to reflood a total of 13,000 acres.
- Operate the Marsh Flow-Way since November 2003 and, through 2009, filter 2.6 times the lake’s volume — resulting in the removal of 62 million pounds of suspended solids and 37,300 pounds of phosphorus.
- Harvest gizzard shad since 1993, and through December 2009, removing more than 125,700 pounds of phosphorus and 374,800 pounds of nitrogen in fish tissue and preventing them from recycling phosphorus by feeding in the lake sediments.
- Replant six native wetland species of vegetation in the water along the lake’s shoreline, which helps restore fish and wildlife habitat.
- Work with the Friends of Lake Apopka and the East Central Florida Regional Planning Council to develop a plan to ensure that future development does not negatively impact the lake
Future improvements are anticipated as more former farms on the lake’s north shore are reflooded. District staff have developed a remediation plan for the North Shore Restoration Area consisting of infrastructure improvements to reestablish independent flooding blocks. Recent soil testing shows that about 3,000 acres need mechanical remediation to reduce contaminant levels to safe levels for fish and wildlife. The USDA is providing matching funds in two cost-share agreements to complete this work. As areas are reflooded, fewer nutrients will be pumped into the lake, accelerating expected improvements in water quality.
Contact information
For additional information about Lake Apopka, contact David Walker, basin program manager, at (386) 329-4833 or dwalker@sjrwmd.com.
Updated on 5-28-2010
