Dam breaching is likely ineffective where major fish passage improvements have already been made, such as on the lower Columbia and lower Snake rivers. Since 2001, the U.S. Army Corps of Engineers has invested close to $2 billion in new fish-passage technology at these dams. They’ve even developed new advancements that are a model for hydroelectric dams around the world. As a result, NOAA Fisheries has found that the operation of these dams is unlikely to jeopardize endangered salmon, steelhead, or orcas.

There are also some concerns about what dam breaching might look like for salmon in the Snake River. It is likely that there would be a severe decrease in water quality from the increased flow of pollution and sediment. Prior studies done by the U.S. Army Corps of Engineers surrounding the 2002 EIS suggest that toxic chemicals and sediment would be released into the river following dam breaching, leading to lower water quality. It is safe to assume that more toxins have built up since then, along with pollution and plastic, and that their release could have a negative impact on salmon recovery.

Bonneville Power Administration Fact Sheet: Many Paths to the Ocean
2019 NOAA Fisheries Biological Opinion
Army Corps of Engineers 1999 “Lower Snake River Juvenile Salmon Migration Feasibility Study”
Amount of trash found in Columbia River cleanup surprised some local divers