What is a stormwater wetland? The man-made feature is created to provide natural treatment of polluted stormwater runoff from nearby impervious surfaces. Pollutants such as sediment, nitrate, and phoshophorus are absorbed by the wetland before reaching the North Fork of the Maquoketa River, The design, topography, and vegetation within and surrounding a stormwater wetland all aid in the treatment of polluted runoff, which degrade aquatic habitats.