Municipal stormwater general permits

Municipal stormwater general permits cover discharges from municipal stormwater systems. These are systems run by public entities that are separated from sanitary sewer systems.

There are four municipal stormwater general permits in Washington:

Phase I Municipal Stormwater Permit

The Phase I Municipal Stormwater Permit regulates discharges from municipal separate storm sewer systems (MS4s) owned or operated by the state's largest cities and counties.

These include:

  • Incorporated cities with a population of over 100,000* people.
  • Unincorporated counties with populations of more than 250,000* people.
*Populations are based on the 1990 U.S. census.

Phase II Municipal Stormwater Permits for Eastern and Western Washington

The Phase II Municipal Stormwater Permits cover the next most populated parts of the state.

We issue two Phase II permits:

Secondary Permittees

The permit also applies to public separate storm sewer systems operated by other types of public entities located in a Phase I or II city or county. Examples include ports, prison complexes, park districts, universities, or diking and drainage districts.

Washington State Department of Transportation (WSDOT) Municipal Stormwater Permit

The WSDOT municipal stormwater permit regulates discharges from state highways, rest areas, park-and-ride lots, ferry terminals, and maintenance facilities within the urbanized areas of the state.

Who's covered under the municipal stormwater permits?

View a map of Phase I and Phase II Municipal Stormwater Permit area boundaries.
Phase I cities and counties
Western Washington Phase II Cities
Western Washington Phase II Counties
Eastern Washington Phase II Cities
Eastern Washington Phase II Counties


For guidance about applying, changing, or implementing and complying with your municipal stormwater permit see the municipal stormwater guidance page. Stormwater manuals provide stormwater permit implementation and management guidance. For more general stormwater permit guidance, see the stormwater guidance page.

Frequently asked questions

Have a question? Check out our frequently asked questions page.

Stormwater monitoring

Are our permits successful at preventing or reducing pollution from stormwater runoff? Check out the Stormwater Action Monitoring program and our other results on the stormwater monitoring page.

Keep in touch with us

Join our municipal stormwater permit listserv to receive updates about our permits.