What kind of baits did you use? I have seen this on my screen before in the winter. Thinking it was shad I threw my cast net over top of them. Big mistake! They turned out to be channel cats stacked in a wintering hole! It took me 2 hours to get about 40 catfish out of my net! It could be large shad or white bass also. Throw a cast net in the water next time and you should get an idea of what they might be.