As land development increases the amount of impervious surfaces such as roads and parking lots in an area, the stormwater runoff from the area increases as well. This increase in runoff decreases the amount of rainfall that seeps into the ground, and increases the flow of water into the nearby streams and lakes, causing local flooding and stream channel erosion. Water quality is affected by the accumulation of trash, oil, and rubber from cars, fertilizers and pesticides applied to lawns, sediment from bare or poorly vegetated ground, and other pollutants entering streams, rivers, lakes and Long Island Sound. Carelessly discarded debris can find its way into the stormwater drainage system, and eventually, Long Island Sound as shown in the photos on the right. Inflow of sediment can cloud water, blocking sunlight from submerged plants. Sediment also settles to the bottom of the Sound , clogging the gravel beds used by fish for laying their eggs. Nutrients, such as phosphorus and nitrogen, from fertilizers enter the water and promote unusually rapid algae growth. As the algae dies its decomposition reduces or eliminates oxygen needed by fish, shellfish, and other aquatic life for survival.

These are all examples of nonpoint source pollution, one of the major contributors to the degradation of the waters of Long Island Sound. Stormwater management controls nonpoint source pollution through the use of structural and nonstructural best management practices (BMPs) to intercept runoff from developed areas, filtering and treating stormwater runoff, and then discharging it at a controlled rate into streams, lakes and ultimately Long Island Sound. Further information concerning Long Island Sound water quality may be found at www.epw.gov/region01/eco/lis.