The Chesapeake Bay watershed covers about 64,000 square miles, including portions of six states and the District of Columbia. Trees filter sediment and nutrients from runoff and their roots stabilize stream shorelines and reduce erosion. By shading the water, riparian forests also reduce summer water temperatures, increasing dissolved oxygen levels. Agricultural land use is mainly divided into two categories - pasture and cropland.
Pasture land consists of grassy areas for feeding livestock.
Cropland is cultivated to provide various food products. Urban and suburban lands provide space for homes, roads, and jobs, but increases the amount of impervious surface area and stormwater runoff. As a watershed becomes more developed, the amount of pollutants in the stormwater runoff increases, as does the amount of wastewater and solid waste requiring disposal. The connection between human activities on the land and Bay degradation is clear. Shifts from environmentally beneficial uses to less desirable uses increase pollutant loads and challenge water quality, habitat and living resource restoration efforts.