Puget Sound Innovation Stories

Capitol Hill Water Quality Project—Swale on Yale

Whenever it rains, untreated stormwater from more than 600 acres of north Capitol Hill, in Seattle, drains directly into Lake Union. Stormwater flows down buildings and across the streets, collecting pollutants before being discharged to the lake. Lake Union is a key stop in the epic lifecycle of this watershed’s salmon population—recent research shows the critical link between stormwater pollution and coho salmon dying before having a chance to lay their eggs.

At least that’s what used to happen. A new Capitol Hill commercial real estate development project offered the City of Seattle a unique opportunity to address many urban challenges at once:  the need for housing, commercial space, historic preservation, a beautiful and inviting streetscape, and the opportunity to cleanse polluted urban stormwater runoff before discharging it to one of Seattle’s most iconic lakes. How? Through biofiltration swales.

The mechanics of the biofiltration swales are simple: During rainstorms, dirty water from storm drains flows through a dense matrix of wetland plants, like rushes and sedges, growing in the swales. The plants filter pollutants out of the water. Now clean, the water is returned to Lake Union.


In sunny weather, the combination of attractive plantings, benches, and pedestrian foot bridges over the swales offer residents and employees a beautiful place to pause, relax, and enjoy the scenery. This project supports the City of Seattle’s efforts to meet the requirements of the federal Clean Water Act in an innovative and cost effective way.

Funding Sources:

  • Seattle Public Utilities
  • Washington State Department of Ecology
  • Vulcan Inc.

Congressional District: 7


  • Seattle Public Utilities (City of Seattle)
  • Vulcan Inc.


Photo credits: Vulcan Real Estate

More Info

Publish Date: April 20, 2017
Category: Stormwater
Congressional Districts: Congressional Dist. 7
Legislative Districts: Legislative Dist. 43
Counties: King
Habitat Types: Puget Sound
Restoration Focuses: Reduce Pollution | Salmon | Water Quality
Funding Sources: