All of these contaminants are carried by stormwater (now known as polluted stormwater runoff) to the nearest storm drain or drainage swale and are eventually delivered, untreated, into the nearest river, lake or stream. This type of water pollution is known as nonpoint source pollution because the sources of contamination come from many dispersed locations that, while each may be very small, cumulatively have a large impact. This is opposed to a sewage spill or industrial discharge, which is known as a point source of pollution.

A common misconception is that water that runs off streets and parking lots into a storm drain goes directly to a wastewater treatment plant. It doesn't. In fact, stormwater usually receives no treatment!

Stormwater pollution can make monitoring and treatment of our drinking water more difficult and costly. In addition, it can hinder the health of the aquatic ecosystem and result in the loss of our rivers, lakes and streams for recreational purposes.