Northern pike would take care of them.
Native species will take care of them. The lake is probably fished out or there would never be that many fry swimming openly.
I collect wild fish for aquariums. The imbecile who does not want to encourage private fish collecting is a twit.
If the lake can be drained it must not have springs feeding it and it must also be landlocked. As such it is fed by rain and maintained by the water table. There probably are no native species in what is likely not a lake but is a large pond.
Or flathead catfish.