I’ve fished many bodies of water where dead fish were visibly present so I’m not saying it doesn’t happen, but there is always a cause. Sometimes pollution, sometimes a hard freeze, aeration or oxygen/carbon dioxide levels,, overheating, choking trying to eat a fish or bird that was too big lol etc..
I’m def no expert but start with getting your water tested. And not just for the basic PH, alkalinity, salinity, ammonia, nitrates, nitrites, etc.. you might send it into a lab to get a full analysis on what’s happening bc you shouldn’t be seeing fish just die off regularly.
