I was at Ventura beach with my kids yesterday (one of whom just graduated from an online high school, so we had to fly to California). The water was very cold. Like, scream-when-it-hits-your-toes cold. So I was delighted to see that there were a couple of crazy people about to throw themselves into the sea. Naturally I got out the trusty Seek Thermal camera I keep in my pocket at all times!
I think it's really interesting that you can see a reflection of their heat output in the water below them. I guess it's not surprising, given that radiant heat is just light, same as any other kind of light. (Water is opaque to thermal energy in this range of wavelengths, so very sadly one could not see any dolphins or seals swimming underwater. But it is able to reflect a much wider range of wavelengths than it can transmit.)
Another curious thing is that the foam on the crashing waves appears much warmer than the water around it. I'm guessing that the foam is reflecting heat from the land, while the smooth water is reflecting the deep cold of the sky. But there might also be some frictional heating of the water by the crashing action. There is, after all, quite a lot of energy being released by this process, and it's all got to end up as heat.