Juvenile salmon and steelhead migrating out of the Columbia River Basin in unusually high flows this year face a potentially lethal problem in spillways at dams where increased nitrogen in the water can cause tissue-damaging gas bubble trauma.
But fisheries managers say special features at dams meant to reduce nitrogen will help young fish make it to the ocean and predict survival this year will be about average based on previous high-flow years.
Like natural waterfalls, water going over a dam's spillway increases total dissolved gas in water. That includes nitrogen that can cause bubbles to form inside fish.
The standard for total dissolved gas considered safe for fish is 110 percent, but dams on the Columbia and Snake rivers in recent weeks have been near or above 120 percent.