Sounds pretty similar to what I have experienced which is a population cycle. We have been through a cycle several times (well documented in earlier threads) where we go from catching large #'s of fish to fighting to catch anything. It seems that the best fishing comes the year before the worst (makes sense if you think about it, they are lowest on food the year before the crash, and therefore feed on anything you throw in front of them).
We also get that same algae / moss growth every summer, with no effect on the fish.
