In the early 1990's, the Federal Clean Water Act required municipalities with populations greater than 100,000 (including areas municipal separate storm sewers located within the boundaries of a region defined by a storm water management regional authority based on a jurisdictional, watershed, or other appropriate basis that includes one or more of the systems) to apply for and obtain a National Pollutant Discharge Elimination System (NPDES) permit for their stormwater discharges.
In Oregon, this program was delegated to the Oregon Department of Environmental Quality (DEQ).
As a result, DEQ directed six Oregon jurisdictions and associated co-permittees to apply for and obtain a municipal NPDES stormwater permit. Clackamas County was one of the jurisdictions required to obtain an NPDES permit, and the City of Lake Oswego is one of the 13 co-permittees on the Clackamas County permit. City of Lake Oswego received their NPDES stormwater permit from DEQ in 1995. The NPDES Permit has subsequently been renewed in 2004 and in 2012.