In developed areas, urban or suburban, a large portion of the land surface is covered by buildings and paved surfaces. This creates sizable areas that rely on storm drains to carry water runoff from roofs and paved areas to nearby waterways. Rather than using the ground as a natural absorbent for rain and snowmelt, the stormwater runoff in paved areas carries pollutants (oil, dirt, chemicals, fertilizers) directly into streams and rivers where they are harmful to water quality.
Controlling damaging runoff by protecting natural areas, using low-impact development strategies and limiting pollutants are key factors in ensuring water quality.