The notion that the Snake River dams massively wiped out salmon runs is simply not true. How do I know? Because Bonneville Dam was down-stream counting fish both before and after the dams went in. And the numbers show no decrease and average steelhead numbers actually went up during this time period (due undoubtedly to the hatcheries put in along with the dam). Now it could be that the ravages of the earlier part of the century wiped out these fish and the dams make it harder for them to re-build, but the dams themselves did not do it.