Welcome, d lee, lots of expert fatheads here, I mean fathead experts, and I'm sure they'll chime in soon. Typically, fatheads reproduce so quickly that the population should replenish itself very fast, even if you did lose a significant proportion over your spillway, which is not likely. What kind of predators do you have in the pond?

N.B. to JHAP--now that's the way to pad your post count, my friend!