I am sure some fish get sucked through the dams and below dams are always good places to fish. But when pouring the water out of a 5 gallon bucket of minnows I have noticed how they always swim in the opposite direction of the water flow therefore staying in the bucket till almost all the water is gone. By saying this I think if a fish didn't want to go through a dam it would be hard to make him because they swim pretty fast when they want to.