Today, they must struggle through the enormous reservoirs behind the dams, where they are exposed to predators, disease and lethally high water temperatures. Many fish die when forced through the dams' hydropower turbines. Costly efforts to collect the young fish with giant screens at the dams and transport them to the ocean by barge have failed to stop the decline. The Corps recently conceded that fish barging would not lead to salmon recovery. The dams also take a heavy toll on adult salmon returning upstream to spawn.
Many salmon have trouble finding the fish ladders on the dams.
Scientists believe that many of the adults that do eventually reach their spawning grounds upstream are often too exhausted from the grueling journey to spawn successfully. Finally, the reservoirs have flooded spawning habitat . The end result has been disastrous for Snake River salmon and steelhead, which are not returning to spawn in sufficient numbers to avoid extinction. In 1999, not a single chinook salmon returned to spawning grounds in two Snake River tributaries. Federal scientists believe that some salmon stocks could go extinct within the decade.