Pond Boss Forums POND CONSTRUCTION Building a dam Dam Erosion

Typically, the only fish that leave are the youngest ones, babies that linger near edges and the surface.
Mature fish, especially bass, bluegill and catfish, tend to stay nearest their cover or food supplies. Heavy flow doesn't trigger fish exodus. Lack of food or cover in a lake gives fish a motive to seek greener pastures (literally).
Putting a screen across a spillway has been known to create enough resistance to flow to force water to seek another path, over a dam. I have seen it happen. When water flows over a dam, it can be catastrophic...not only for the dam and lake, but for anything in the way downstream. No screens rising higher than 10 inches lower than the lowest point of a dam.