It’s crazy. Before I paid attention to water temps when I was a kid, I assumed the max temps a lake might get would be 75-80.
Part of that might have been from raising tropical fish where 75 was a good normal temp, while I would bump it up to 80 when breeding them. If you pushed the temp much higher than that the fish would die of stress.
I suppose while surface temps might be that high, you get more reasonable reading the deeper you go, depending on the lake depth.
I wonder how the fish are doing on Knife Lake outside Mora. The vast majority of the lake is about 8′, with the main basin being about 12-13 average with 14′ max.