Exactly, which is why worrying about the amount of water being used is kind of a moot point with the dams in place. The only way to restore the runs is to dynamite them all, which will never happen because everybody (including the city folks that are so worried about farmers using all the salmon water) depend so heavily on hydro power. That's why it's a feel good thing. They want to feel like they're doing something to preserve/restore the runs, when the only way to actually do it is sacrifice the hydro power they're benefiting from, flood out a bunch of communities downstream, and leave the farmers with zero water.
Even the dams with fish ladders have problems. The young salmon trying to go downstream are pureed when they hit the turbines.
It's too bad the tesla disk turbine wouldn't work on that scale. The fish would actually have a shot then, they'd just shoot through the turbine no harm done.