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Sewage Overflow Prevention

Protecting Seattle’s Waterways


Seattle waterways will benefit from upcoming projects to prevent sewage overflows and polluted stormwater runoff.

Every year, rain washes millions of gallons of untreated sewage and stormwater into the city’s waterways, threatening human and aquatic health and our quality of life. Each year, on average, more than 300 sewage overflows send millions of gallons of raw sewage and stormwater into Seattle’s creeks, lakes, the Ship Canal, the Duwamish River, and Elliott Bay. These combined sewage overflows (CSOs) create significant health and environmental risks.

The Plan to Protect Seattle's Waterways

The draft Long-term Control Plan, draft Integrated Plan, and draft Environmental Impact Statement (DEIS) are available. Read the
Plans and Impact Statement.

Seattle Public Utilities is evaluating two alternatives in the Plan:

Integrated Plan stormwater projects

  • Expansion of street sweeping on arterial streets (citywide)
  • New stormwater quality facility (South Park)
  • Natural Drainage Systems Partnering (Piper’s, Thornton, and Longfellow Creek drainage areas)

Read the Community Guide to the Integrated Plan (pdf)

More detailed information: