Stormwater ponds are designed to capture and treat pollutants from runoff. Whenever it rains, stormwater rushes over impervious surfaces such as streets, sidewalks, roofs or parking lots and rapidly transports contaminants such as oils, salt, pesticides, heavy metals, and pathogens to these ponds. Stormwater runoff also delivers nutrients from pet waste, fertilizers, grass clippings and sediment to the ponds causing algae blooms and green coloring. Pollutant build-up in a pond is often an indication the pond is doing exactly what it was designed to do.