Western Washington Phase II Municipal Stormwater Permit

We develop and administer Clean Water Act National Pollutant Discharge Elimination System (NPDES) municipal stormwater permits in Washington. The Western Washington Phase II permit requires local governments to manage and control stormwater runoff so that it does not pollute downstream waters.

The current permit is effective Aug. 1, 2019, and expires on July 31, 2024.

Current permit documents

Supporting documents

Overview of permit timelines

View permit timelines for new and continuing permittees. These timelines provide an overview of major deadlines for implementing permit requirements.

Annual reports for the calendar year are due by March 31 the following year.
The Manchester Stormwater Park, with a catch basin surrounded by small rocks and plants.

Am I covered by a MS4 permit? 

The Phase II permit for Western Washington covers over 80 cities and portions of six counties.

Find a list of cities and counties covered by this 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

Permit history

Keep in touch with us

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