As for the salmon, are there more salmon in the river now? Or were there more before the dams were built? The corp of engineers seem to be putting an awful lot of effort into making the dams “transparent” to fish migration.
The fish are counted at each dam by swimming past a window and tallied by a trained fish counter. ( trained to identify types of fish).
There are several fish hatcheries so some runs are more than the wild populations of the pre-dam fish. Indians claim the hatchery fish aren’t as good as wild fish so you can’t satisfy everyone.
The Panama Canal wouldn’t work if water wasn’t renewable as rainfall refills the lake the ships travel through on the top of the hill on the isthmus.