Army Corps Required to Limit Hot Water Pollution from Lower Snake Dams

Published 11/17/2021  |  Idaho Rivers United

In September the EPA issued discharge permits to the Army Corps of Engineers that will limit hot water and oil pollution stemming from the four Lower Snake River dams. This is a significant step in the effort to cool down river temperatures that are lethal to migrating salmon and steelhead. The Corps, which operates the dams, will now be held accountable for hot water conditions on the Lower Snake that last weeks on end in the summer and threaten salmon runs returning to Idaho.

The permits come into effect next spring and are the culmination of years of work by IRU and our partners Columbia Riverkeeper and Advocates for the West. Last summer, the EPA issued a total maximum daily load (TMDL) plan for the Columbia-Snake River corridor, which is designated as an impaired body of water by both Washington and Oregon. The TMDL identified the dams on the Columbia and Lower Snake rivers as the main cause of warming, along with climate change since the 1960’s. The plan acts as a pollution budget for the river, and sets out water temperature reduction targets.

The permits now require the Corps to implement temperature reduction strategies on the Lower Snake. Reservoir drawdown and other structural changes may be required to meet the targets outlined in the TMDL. According to the EPA’s temperature model, a free-flowing Lower Snake River would be significantly cooler in the late summer than the current degraded dam-reservoir environment.

Salmon and steelhead migrating upstream to Idaho must contend with prolonged hot water conditions in the reservoirs, which are consistently over the 68 degrees Fahrenheit threshold that is considered safe for salmonids. Hot water exposure causes stress, lesions, and disease, eventually becoming lethal for salmon. This summer was exceptionally hot, leading to thousands of salmon dying in the river before reaching upstream spawning grounds.

Idaho’s wild salmon and steelhead are endangered and on a trajectory towards extinction. The discharge permits for the four Lower Snake dams represent an important step towards alleviating water temperature issues on the river. Much work remains to be done in order to restore the Lower Snake River and place wild salmon on a path to recovery.

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