We develop and administer Clean Water Act National Pollutant Discharge Elimination System (NPDES) municipal stormwater permits in Washington. The permit requires local governments to manage and control polluted stormwater runoff so that it does not pollute downstream waters.
Stormwater is rain and snow melt that runs off surfaces such as rooftops, paved streets, highways, and parking lots. As water runs off these surfaces, it can pick up pollutants that contaminate local water bodies.
The Phase II permit for Western Washington covers at least 80 cities and portions of five counties. It is effective as of Sept. 1, 2012.
Am I covered by a MS4 permit?
Find a list of cities and counties covered by this permit.
Current status of of the permits
The Western Washington Phase I and Phase II permits expire on July 31, 2018. After careful consideration of many factors, we have decided to extend the current (2013-2018) Western Washington Permits for one year. The permits will reissue on July 1, 2019, and become effective Aug. 1, 2019 through July 31, 2019.
We are in the process of re-issuing both Western Washington Phase I and Phase II Municipal Stormwater permits.
Western Washington Phase II Municipal Stormwater Permit
Municipal stormwater permit guidance
For guidance about applying, changing, or implementing and complying with your municipal stormwater permit see municipal stormwater guidance. 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.
Annual Reports for the calendar year are due by March 31 the next year.
How well do our permits prevent and reduce pollution from stormwater runoff? Check out the Stormwater Action Monitoring (SAM) program and our other results on the stormwater monitoring.
Keep in touch with us
Join our municipal stormwater permit listserv to receive updates about this permit.