can the water temperature in a lake change overnight?

Answer 1

Yes. During the fall, it's overnight that the temp decreases the most. (Sometimes also during the day if the weather changes and a cold north wind starts up.) The decrease at night is due to several factors - cooler air, wind, but radiation of heat to a cloudless night sky is significant. So it generally starts one morning a tiny bit cooler than the previous morning.

During the spring when the temp is increasing, it's not so likely to happen at night.