OK, happened again, exactly one year later: end of autumn, start of winter. I’ll just let it play a little and see what happens.
Edit. Hmm, on closer inspection, it occurred only on one lake this time (the largest). If it was over-fishing, I’d expect the little ponds to be hit first…
And it’s resolved itself again after less than a month this time.
Edit again: A week later, back to no fish. So it’s turned off, on, and off again for the largest lake all inside a single month.
What I find interesting - and rather surprising - is that there are huge lakes that get fished out within a year and there are only three fishermen assigned to it. Comparatively, there is a small pond nearby that has just many fish that has one fisherman assigned that also gets fished out within a year.
Proportionately there should be FAR more fish in a giant lake compared to a tiny pond but there doesn’t seem to be. It should take a very long time to fish out a huge lake but with reproduction levels, etc. of the fish this should never happen unless the entire lake is surrounded by fishermen.
Hopefully this will be looked into further in the future.