The Basics

The problem:
As rain runs off streets, rooftops, and parking lots, it picks up oil, grease, metals, and other pollutants, carrying them to our lakes, creeks, the Duwamish River, and the Puget Sound. In many parts of Seattle, rain also flows into the sewer system. During storms, this rain can cause sewage overflows into local waterways. Recent scientific studies have determined that polluted runoff is the biggest threat to water quality in the Puget Sound.


oil gas rainbow stormdrain

A solution: Green stormwater infrastructure (GSI) makes our homes and neighborhoods more green and slows, captures, and cleans polluted runoff from roads, roofs, and parking lots at its source, before it harms our waterways. We can put green stormwater infrastructure on private property to add attractive landscaping and help slow and clean polluted runoff from roofs, patios, and driveways.
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We can put green stormwater infrastructure in our public spaces—such as planting strips next to the street—to add beauty to our urban neighborhoods and help soak in and clean stormwater that would otherwise run off streets, sidewalks, and parking lots. Types of GSI include:

  • raingardens
  • bioretention
  • green roofs
  • permeable pavement
  • cisterns
  • trees
 GSI roadside rain garden


GSI in Seattle

Seattle GSI


Seattle is a national leader in using GSI. We have been building GSI for nearly two decades. This picture shows a High Point rain garden (in the West Seattle neighborhood) that helps keep polluted runoff out of Longfellow Creek. Seattle has a goal to manage 700 million gallons of polluted runoff by 2025.


Partners & Contributors

Thanks to the contributions of many community partners, philanthropies, private developers, and Seattle Public Utilities and King County Wastewater Treatment Division, nearly 100 million gallons of polluted runoff are managed by green stormwater infrastructure in Seattle.


Below are links to organizations that have been involved with building GSI in Seattle. If your organization would like to be added to this list, contact us.