I think in the winter it would be fine to move heat from the lake to houses but in the summer it's worse. We're already having problems with lakes being too hot in the summer which results in evaporation, algae build-up and less oxygen. This also promotes invasive species.
Of course, the question is at what scale we can build such systems and if that would raise water temperatures significantly.
Of course, the question is at what scale we can build such systems and if that would raise water temperatures significantly.
I am not a biologist.