Rafts covered with soil and plants are anchored in the lake to create floating garden “wetlands” that clean the water. The plant roots grow through the raft bottom into the lake, where they absorb nitrogen and phosphorous. Bacteria create a biofilm on the raft and roots that consumes nitrogen and phosphorous, converting them to less harmful substances.
Pollutants such as metals and particulates are also filtered out, since suspended solids bond to the biofilm. This makes the water clearer, which lets light penetrate deeper, thereby letting plants grow deeper, bringing oxygen deeper. Organic matter that attaches to the underside of the floating islands provides food for fish, and the islands provide habitat for birds. Planting floating gardens with commercially valuable plants can increase the impact of this project.