Numerous sources of water pollution that have come under control the last 25 years. However, stormwater runoff is mostly untreated and is now a significant source of pollution. Stormwater runoff occurs when rainfall or snow melt runs over land — picking up pollutants along the way — and deposits the polluted runoff in our lakes and streams. This is a concern in Southeast Michigan and other areas of the country. It will continue to be a challenge as our region develops. This is largely due to the growth of impervious surfaces, for example, roads, parking lots, rooftops, and buildings. Increased impervious surface adds to the amount and rate of pollutants in our stormwater. Developing communities and older communities alike are challenged with reducing these stormwater impacts to protect Southeast Michigan's valuable water resources.