When I worked for the city water plant, we regularly stocked "Grass Carp" in the two 5 acre reservoirs we managed to help keep down algae.
We drained the lakes about once a decade and usually had pickup truck loads of 2 inch bluegills, a few 4 to 6 pound largemouth bass, and maybe one or two 25 pound grass carp come out the drain.
We once had a 25 pound grass carp come into the treatment plant through the intake pipe in the middle of the night. The racket made as he hit the mixing propellers about scared the solo night workman to death.