Stormwater is rain and snow melt that runs off rooftops, paved streets, highways, and parking lots. As it runs off, it picks up pollution like oil, fertilizers, pesticides, soil, trash, and animal manure. Most stormwater is not treated, even when it goes into a street drain. It flows downstream directly into streams, lakes, and marine waters.

Stormwater runoff is the leading threat to Washington's urban waters, streambeds, banks, and habitats. 

Why does stormwater runoff matter?

As the population grows in Washington, urban development increases. This means more people, more developed land, and an increase in stormwater runoff and pollution to Washington's waters.

Unmanaged stormwater runoff can:

  • Damage salmon habitat.
  • Contribute to flooding and drought.
  • Contaminate swimming areas.
  • Pollute shellfish beds.
  • Contaminate the groundwater you drink.
  • Degrade water quality.

What are we doing about it?

We issue permits under federal and state laws to control surface and groundwater pollution from runoff. The most-populated cities and counties, as well as industrial sites, construction sites, and many businesses have stormwater permits.

We also:

  • Provide guidance and technical assistance on how to comply with permit requirements.
  • Monitor results to show how well we are doing.
  • Enforce as a last resort when pollution limits in permits are not met. Penalty fines that we collect go to the state’s general fund or to dedicated pollution prevention accounts. 
  • Provide funding for stormwater improvement projects.

What types of permits are there?

The federal Clean Water Act's National Pollutant Discharge Elimination System (NPDES) has various permitting requirements based on different types of pollution discharges.

Both NPDES and State Waste Discharge stormwater general permits aim to control pollution discharges to water. For more information, see stormwater general permits.

Our permits include:

Stormwater guidance & databases

Go to our stormwater permittee guidance page to learn more about applying, changing, implementing, and complying with your stormwater permit.

Stormwater databases

Stormwater monitoring

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

This bioretention facility helps filter water that runs off pavement before it enters the stormwater drain.