Retention ponds are designed to manage stormwater flow and trap pollutants. Because many collect a significant amount of nutrients, the ponds often grow algae on the surface of the water. This can create odor concerns and lead to low oxygen levels that do not support aquatic life. The floating wetlands are essentially buoyant mats that can be filled with plants. The plants help remove water through evapotranspiration and filter pollutants. They also provide habitat and help prevent ponds from developing low oxygen conditions. Read more.