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Upward of 2.5 million wild salmon once populated the rivers and streams of the Snake River basin in Idaho. Today, all of Idaho's salmon species are listed as threatened or endangered under the Endangered Species Act. There are many factors that affect salmon throughout their life cycle, but the main reason for their sustained decline is dams.
Since the completion of the four lower Snake River dams in particular, the populations of Idaho's salmon have crashed.
How dams kill salmon
Dams and their reservoirs pose the most daunting problem for juvenile salmon (called smolts) during their migration to the ocean:
- Smolts rely on a river current to flush them downstream during spring runoff months. Dams still the river into reservoirs. Without a guiding current, smolts have difficulty finding their way downstream.
- Reservoirs warm water temperatures, which stresses smolts.
- Stressed and confused smolts are easy prey for birds and predatory fish that thrive in reservoir environments.
- Some smolts are caught in dams' deadly turbines.
- Dams and reservoirs cause the smolts journey to take much longer, disrupting the biological transformation -- from fresh water to salt water -- which salmon undergo. Historically, the migration would take 10 to 20 days. Now it can take months for a baby salmon to reach the ocean.
- Adult salmon migrating upstream must climb stair-step ladders to get over 8 dams plugging the Columbia and the Snake. Scientists estimate that between 15% and 30% of returning salmon die during the passage through eight fish ladders and reservoirs.
- Dams and reservoirs are the single biggest killer of Idaho's salmon.
Four dams too many
Smolts are able to make it past a few dams and reservoirs on their outward journey. But the cumulative effect of passing eight dams and going through eight reservoirs is too stressful. Fisheries biologists say that removing just the four lower Snake River dams will give wild salmon the fighting chance they need to recover.
For example, in the late 1950s before construction of the lower Snake River dams, Idaho's salmon had to navigate only three dams on the Columbia River. Salmon populations were relatively healthy back then, even though they had to deal with a few dams.
But between the early 1960s and mid 1970s, one more dam was added to the Columbia and four to the lower Snake River that made their journey twice as treacherous. After the last dam on the lower Snake was completed in 1975, Idaho's salmon populations began a trajectory towards extinction that continues today.
For years, a majority of fisheries biologists have said that the surest, and probably the only way to restore Idaho's wild salmon populations is to remove the four lower Snake River dams. ---->>>Learn more about dam removal |
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