[vanderZwan]

I think that's the wrong way round: climate change causes longer summers and shorter winters, so the problem is one of cooling, not heating.

Shade balls[0] could work, but then they'd have to cover part of the lake with that.

EDIT: And of course, that also comes with a reduction in total light reaching the lake, which may have different side effects beyond temperature alone.

[0] https://www.youtube.com/watch?v=uxPdPpi5W4o

[cnnlives3855]

I think what they’re saying is that if you have sufficient heat at the bottom, hotter water rises, so you get cycling.

[vanderZwan]

Look at the full picture. The cycling is reduced due a reduction in temperature gradient. That reduction in temperature gradient is due to water not cooling down enough in winter and warming up for longer in summer.

Could you increase cycling by creating a temperature gradient by capturing the heat from the sun to warm up the water at the bottom of the lake? Maybe, but that also would imply an even greater increase of average water temperature than the effects of climate change. Which would have all kinds of other ecological side-effects.

Or put another way: global warming increases thermal energy being added to the system, resulting in a change of the dynamics of the lake. Cooling it would counteract that increase. Capturing more heat would add even more thermal energy. Even if they both could affect cycling in the same way, adding even more thermal energy is almost guaranteed to create other ecosystemic imbalances.