There is a link between impervious surfaces within a watershed, (here we see a subset of the Chesapeake Bay watershed area) and the water quality within the watershed. In general, once 10-15 % of an area is covered by impervious surfaces, increased sediments and chemical pollutants in runoff have a measurable effect on water quality. When 15-25% of a watershed is paved or impervious to drainage, increased runoff leads to reduced oxygen levels and impaired stream life. When more then 25% of surfaces are paved, many types of stream life die from the concentrated runoff and sediments.