The Lake Apopka Marsh Flow-Way is a constructed wetland located along the northwest shore of Lake Apopka and west of the Apopka-Beauclair Canal. Its purpose is to filter algae, suspended sediments and associated nutrients from Lake Apopka’s water, hastening the recovery of water clear enough to support submerged vegetation on the lake’s bottom. This recirculating system filters about 40 percent of the lake’s volume each year. It began operation in November 2003 and joined the ongoing rough fish harvest as projects removing nutrients from Lake Apopka.
The system covers approximately 760 acres and contains four individual wetland cells, in addition to levees, canals and ditches. Prior to construction, the area had been farmed for decades, during which time many feet of organic soils had been lost. Now lake water flows by gravity from west to east through an individual cell, before it is collected in the pump basin and lifted back up to the Apopka-Beauclair Canal. Most of the cleaner, treated water returns to Lake Apopka, while the remainder flows downstream toward Lake County Water Authority’s nutrient removal facility (NuRF) and Lake Beauclair.
The dominant vegetation growing in flow-way cells are shallow marsh and shrub swamp species, including species such as pickerelweed (Pontederia cordata), arrowhead (Sagittaria lancifolia), cattail (Typha sp.), while shrub swamp areas have primrose willow (Ludwigia peruviana) and some willow (Salix).
As incoming lake water passes through the Marsh Flow-Way’s shallow cells, the emergent vegetation slows water velocity, causing suspended particles and algae containing phosphorus and other nutrients to settle out. These accumulated organic particles, along with decayed wetland vegetation, continuously form new sediments, which store the filtered nutrients. It takes water two to seven days to flow through the system.
Like all ecologically engineered systems, the water quality treatment performance of the flow-way is seasonally variable. Typically, best performance is in cooler months (October through May), while performance is poorer during warm months (June through September). Over its lifespan, system performance has met initial predictions, but has predictably declined as the lake’s water quality has improved.
Upon initial start-up, phosphorus and suspended solids removal rates increased annually, due to increased flows through the system. After 2008, it was determined that too much water was causing erosion, and flows were reduced to allow for better treatment and reduced erosion. Treatment efficiency began to decline in 2015, and damage from Hurricane Irma further decreased treatment efficiency. Maintenance began in 2019 to re-level the wetland cells and reopen ditches which promote sheetflow conditions in the cells. All cells are expected to be back in operation in 2022. Through December 2018, the system removed about 32 metric tons of phosphorus from Lake Apopka, or an annual total phosphorus removal rate of 2.2 metric tons per year. The system also helped clear Lake Apopka’s water by filtering 4,300 metric tons of total suspended solids annually.