Green Bridges for Salmon

The Aurora Bridge Project and the 5 bridges of the Seattle Ship Canal

Welcome to Salmon-Safe’s Green Bridges initiative! We’re happy to introduce our new approach to bridge infrastructure: Green Bridges. In collaboration with our NGO partners and environmentally innovative public jurisdictions and developers, Salmon-Safe is helping to lead the charge in transforming bridges into eco-friendly corridors that help safeguard the health of migrating salmon and enhance the resilience of our transportation systems.

Salmon-Safe bridges incorporate green stormwater infrastructure (GSI) elements like vegetated swales to help capture and filter stormwater runoff. This reduces the flow of pollutants like sediment, heavy metals, and hydrocarbons into waterways, including 6PPD-Q, the toxic tire dust that emerging science has indicated is toxic to salmon and other aquatic life. Whether the project is the design of a new bridge or retrofitting an existing bridge to reduce water quality impacts, Salmon-Safe’s approach to bridge infrastructure was inspired by a partnership at Seattle’s Aurora Bridge.

For 80 years polluted runoff from Seattle’s Aurora Bridge has impacted Puget Sound’s migrating salmon.

Contaminated stormwater from Seattle’s Aurora Bridge was discharged untreated to Seattle’s Lake Washington Ship Canal, impacting migrating salmon and resident orcas that depend on those salmon as a primary food source. That inspired environmentally innovative developer Mark Grey to join forces with Salmon-Safe to convene a multiple organization partnership to treat runoff through rain gardens, including at his Salmon-Safe certified Data 1 development project adjacent to the bridge.

Together with our partners, Salmon-Safe created a blueprint for managing the 2 million gallons that flow directly from the Aurora bridge into the ship canal between Lake Union and Puget Sound every year and, at the same time, developing an innovative model for a public-private partnership addressing contaminated stormwater from Pacific Northwest bridges.


Funded in part by Boeing, the Aurora Bridge project worked through  the following nonprofit partners: Salmon-Safe, Clean Lake Union, and The Nature Conservancy in Washington. Primary technical partners included  KPFF and Weber Thompson. For more information, please contact our project manager Ellen Southard.

How to treat 2 million gallons of bridge runoff?

Building on the success of the Aurora Bridge project, Salmon-Safe seeks to expand work to other bridges on the Lake Washington Ship Canal. Our Green Bridges Pilot Study included the Ballard Bridge, Fremont Bridge, I-5 Bridge, University Bridge, and Montlake Bridge. With green infrastructure in mind, the scope of work was to determine the functionality of the existing runoff collection system, to quantify the extents of the collection basins, to develop new low impact development runoff collection and treatment strategies, and to locate adequate treatment sites. In all, our team determined that with this commitment to bioretention we could collect and treat 98 million gallons of runoff per year and reduce the detrimental impacts that bridge runoff has on this important salmon migration corridor.

Approximately 98 million gallons of untreated stormwater enter the Lake Washington Ship Canal by way of roadway runoff from the six bridges that span the waterway.

On Earth Day 2019, Salmon-Safe and our partner Clean Lake Union were awarded Green Globes, King County’s highest honor for environmental achievement, for the Aurora Bridge Project. “Imagine a world if…all the water was clean enough for salmon to thrive, orcas to live long lives and all humans were safe from pollution; a place where children can swim without fear of toxins in water that is so clean and clear it’s the color of turquoise ice,” said King County Executive Dow Constantine, in presenting the award to Salmon-Safe project manager Ellen Southard, the creative inspiration behind the project, and the entire implementation team.


Seattle Green Bridges Implementation Partners