Aurora Bridge Swales

In the Fremont neighborhood of Seattle, a multi-phase stormwater cleanup effort is setting a new precedent for how cities and communities around the world can tackle challenging toxic stormwater runoff problems.


Clean Lake Union & CoU, LLC


Seattle, WA


Landscape Architecture

ProJECT Overview
  • Project seeks to mitigate over 98 million gallons of polluted runoff entering Lake Union
  • Research from a UW researcher showed that green stormwater infrastructure could neutralize the lethal effects of the pollution, and a larger effort was born to take action to improve our local waterway
  • The bioretention cell cleans and slows stormwater redirected from the Aurora Bridge via the DATA 1 and Watershed swales on Troll Avenue
  • Steel diversion walls within the stormwater cell illustrate some of the fish species that benefit from the improved water quality
Completion Date



Salmon-Safe Certification


ULI Global Awards for Excellence
2023 Winner

ULI Americas Awards for Excellence
2023 Winner

2022 GRAY Magazine Awards
Grand Winner: Landscape Design

2022 Gold Nugget Awards
Merit Award: Best Landscape Architecture for a Community

2022 WASLA Awards
Honor Award
General Design, Private Ownership

2019 Gold Nugget Award
DATA 1: Grand Award Winner
Best Landscape Architecture for a Community

2019 King County Green Globe Award
Salmon-Safe and Clean Lake Union
Leader in Water Quality Solutions

2018 WASLA Awards
DATA 1: General Design, Private Ownership

Seattle 2030 District’s 2017 Vision Awards
DATA 1: Vision Award for Water


Rachael Meyer
Landscape Architecture Principal

PHOTOGRAPHY: Weber Thompson, Meghan Montgomery/Built Work pHotography, Justin weber

How it began

As part of the Data 1 Office project, the design team learned of the lethal effects the runoff was shown to have on the region’s salmon, five species of which swim below the bridge during annual spawning runs. Research from a UW researcher showed that green stormwater infrastructure could neutralize the lethal effects of the pollution, and a larger effort was born to take action to improve our local waterway.

A perfect partnership

In collaboration with the DATA 1 and Watershed client, CoU, LLC, the green rating system Salmon-Safe, and KPFF’s civil engineering team, Weber Thompson has helped spearhead this multi-phased effort to improve the health of Lake Union. The Aurora Bridge, Washington State’s historic 1932 structure which funnels Highway 99 traffic north and south, has been found to have runoff six times more toxic than the national standard. This bridge runs directly adjacent to both DATA 1 and Watershed, and the client decided to tackle the challenge head-on.

A simple solution

Innovative stormwater retention cells have been installed in the right of way at both DATA 1 and Watershed, extending the landscape for the buildings and creating lush green spaces where dark, damp under-bridge sidewalks previously dominated. The planters are filled with vegetation that naturally scrubs stormwater, allowing dissolved pollutants to settle before the water – much cleaner than before – is diverted back into Lake Union.

Photo of Aurora Bridge Swales Phase 3

A public-private model

The first two phases of this work were financed by the DATA 1 and Watershed client. Now, a third phase has been completed across North 34th Street thanks to a non-profit, Clean Lake Union, which was created to advocate for continued clean up efforts around the lake. Additional funding and advocacy has come from The Nature Conservancy and the Boeing Company. Together, these three phases treat up to two million gallons of water annually from the entire north span of the Aurora Bridge.

An agent of change

The Aurora Bridge Swales Project is an exciting new model. The work has inspired additional investigation to size and locate infrastructure for the south span of the Aurora Bridge, as well as the five other bridges that cross Lake Union. All totaled, this project seeks to mitigate nearly 2 million gallons of polluted runoff from entering Lake Union.

“This project is cleaning some of the dirtiest rainwater runoff — and providing benefits to those who live, work and play in this neighborhood.”

The Nature Conservancy

“We have been testing the stormwater as it comes through the bioswale, and even just reaching three chambers of a six chamber bioswale, over 70% of the pollutants have been removed.”

Ellen Southard, Project Partner

“What I love about the bioswales is that [they’re] really cool to walk through. It’s not just about treating the water, but also having people learn about how the water is treated.”

Joanna Callahan, Client

Aurora Bridge Swales in the News

Seattle expands bridge bioswale projects
Engineering News-Record
February 20, 2020

Rain gardens clean pollution on Seattle’s Aurora Bridge
King 5 News
May 27, 2019

Rain garden to filter stormwater runoff from Aurora Bridge
Q13 Fox News
September 20, 2018

How to filter 2 million gallons of stormwater from the Aurora Bridge
The Nature Conservancy
November 27, 2017

Helping out salmon in Fremont, Seattle, WA
The Bramble Project
August 17, 2017

Rethinking the right of way
Huffington Post
May 19, 2017

Stormwater management: Lessons from our forests
Sightline Institute
May 15, 2017

Catching the green wave
Seattle Business Magazine
August 1, 2016

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