I'm going to show the complementary photo first:
|The "overflow dam" of the hydro power plant.|
Here's the photo that sparked my imagination:
|Fish ladder to get past the hydro dam.|
Compare the pictures. First is the hydro dam. Effective at getting as much water as possible through the turbines. Not very pretty and definately unappealing to fish. Height difference is too big for them to jump, and they can't get through the turbines.
The fish ladder looks nice, even in April. Fishes like it, obviously. The route is certainly navigable for them. And the web camera shows that salmons etc. use it too. If it wasn't for the ladders, there'd be no salmons upstream!
The dam is a barrier, like a railway tracks or highway without underpasses. Or any street which does not have a safe way for cyclists and pedestrians to cross it or ride/walk along it. The barrier stops people from moving. It kills active, human powered transportation.
One could also compare the fish ladder to bikeways. One might imagine that a few, strong and fearless fish might survive the dam. But the fishladder? Can you see the small fishes cycling to school and the old granma fishes cycling to bingo, with no danger from the turbine blades?