Threat: Outdated Dam and Floodplain Management and Pollution

The Green-Duwamish River flows from the Cascade Mountains north of Mt. Rainier, winding through farmland and the Seattle — Tacoma metropolitan area, before reaching Puget Sound. Decades of pollution, floodplain development and harmful dam operations have taken their toll on the river and its salmon and steelhead runs.

Two key actions this year can put the river on the rebound: the U.S. Army Corps of Engineers must build a long-delayed system for young salmon and steelhead to migrate downstream past a large dam, and governments at all levels must work collaboratively to manage the river for the benefit of salmon and communities.

About The River

From its headwaters at Stampede Pass in Washington’s Cascades, the Green River flows 30 miles through forested mountains before running into two dams: Howard Hanson Dam, a U.S. Army Corps of Engineers flood control facility, and Tacoma Headworks Diversion Dam, which diverts drinking water to the City of Tacoma. Tacoma’s dam has completely blocked federally-threatened salmon, steelhead and bull trout migrating upstream since 1911.

Below the Tacoma Headworks, the river provides some of the Puget Sound Basin’s best salmon and steelhead spawning habitat as it flows through forests, farms, and the scenic Green River gorge.
At the City of Auburn, the Green River’s fast flowing currents transform into a slower urban river that is channelized and walled off from its floodplain for about 20 miles. Finally, before it enters Seattle and nears Puget Sound, the Green flows through an estuary and its name changes to the Duwamish River.

This transition zone from fresh to saltwater, which provides a critical nursery for young salmon as it bisects diverse neighborhoods, is scarred by decades of industrial pollution.

The Threat

In recent years, as few as 800 Chinook salmon have returned annually to the Green-Duwamish, and for the past 40 years wild Chinook returns have averaged less than 10% of the historic average adult return of 38,000. Nearly half the historic salmon habitat in the Green-Duwamish watershed lies above Howard Hanson Dam.

Tacoma’s diversion dam is already outfitted to pass adult salmon and steelhead above both dams, but experiments with downstream fish passage have shown that it is not worth sending adult fish above the dam until the juveniles can safely migrate downstream through the reservoir and structure of Howard Hanson Dam. Without access to the abundant, forested spawning habitat above the dam, salmon and steelhead recovery will remain compromised.

At the same time, the lower Green River floodplain has been heavily developed, crowding out habitat and putting people and property at risk from flooding. Currently, the river is tightly confined inside an extensive levee system that requires costly maintenance and repair. A severe lack of shade along the river has led to unhealthy, and even lethal, water temperatures for salmon. A comprehensive plan to set back levees and provide a vital buffer of shade trees can help address these development impacts. Furthermore, polluted runoff is already the biggest water quality issue in Puget Sound and across the state. A nearly $350 million effort to clean up the Duwamish must continue to move forward, and polluted runoff from roads and developments must be managed to avoid re-contaminating the river.

What Must Be Done

The National Oceanic and Atmospheric Administration (NOAA) has been calling for the U.S. Army Corps of Engineers to complete the Howard Hanson juvenile fish passage system since 2001. Now the Army Corps and NOAA are discussing a new plan that would complete the fish passage project by 2021, with interim downstream passage provided until then. The Army Corps must commit to this timeline in 2016 in order to assure a future for salmon in the Green-Duwamish River.

In addition, local, state, and federal governments should embrace an integrated management and funding plan for the Green-Duwamish River that provides a path toward funding the fish passage, habitat, shade protection, and pollution prevention actions necessary to restore the river and its fisheries to health. While restoration efforts through a local watershed forum and King County’s recent Green-Duwamish Watershed Strategy to coordinate work and leverage resources are laudable, more political leadership is necessary to restore the river’s floodplain. In 2016, local leaders will decide whether to finally pursue a comprehensive, science-based flood management strategy that includes a long-term restoration plan. On the pollution prevention front, local governments and corporations are working on cleaning up a legacy of industrial pollution in the Duwamish, but a more robust and reliable funding source is needed to adequately control polluted urban runoff.