I sometimes fish a small pond a friend owns. This pond used to have some lunker bass, big bluegills, a few blue & channel cats, and one monster flathead catfish. It also produced a crop of bluegill each spring, and small ones were easy to catch about any time we fished.
3-4 years ago the landowner had a heavy alge bloom and treated the pond with herbacide. The alge died, but it was such a massive shock to the pond it caused it to "turn over" (rotting alge depleated the oxygen level).
He lost many fish over 2-3 pounds in the kill.
Since then I've stocked a few small channel cats for him, and there were small bass & bluegill left.
The past year (and this year) the pond suddenly seems to give up very few fish to my efforts, though. The bluegill I do catch are large (8"+), but I get almost no small ones? The bass seem to be thick, but they also seem to be stunted?
The water is clear and there is a good growth of coontail on the bottom in the shallow water.
Haven't caught a single catfish, caught a few large 'gills, and the bass are the most frequent catch, but no big ones?
Got a couple bass this morning, both about the same size, and only one (8"+) bluegill. They hit very softly, but fought a good fight when hooked.
Took a pic of the bass -
(does it look undernourished to you?)