system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are there warm and cold spots in bodies of water when out swimming?

What causes this. Was out swimming today and I have always wondered but have never been able to figure it out.

Edit: I was swimming in a lake.
gpt
Not an expert, but any chance you were swimming in a lake? There is a phenomenon known as "lake turnover" where the deeper (colder) water rises to the surface. This mostly happens in the summer because of the differences in density between the hot surface water and cold stuff down below.