living up here on the banks of the mississippi river i can tell you guys they will ruin crappie habitat quickly. one thing ive noticed is when we catfish the river in the summer we use throw nets to catch shad. most of the time the young silvers are mixed in with the shad. if you aren't paying close attention you can easily get them mixed up especailly if you catch a mess in one throw. flatheads seem to prefer live shad so we try to weed out the silvers and kill as many as we can but it makes no difference. point i'm making is if a catfisherman goes to lower lake to catch shad and then take his haul up to the main lake it could just snowball from there.