Heh... when i was a kid we'd go surfing at the mouth of the San Gabriel River in Southern California. During the winter the ocean temperature could get into the low 40's which can freeze your ass off even with a full wet suit on, but the mouth of the river was in the low 70's due to 6 or 8 natural gas fired power plants about a mile upriver. They used ocean water to cool the turbines, and that water was then dumped out into the river. never had any issues except for the occasional sea lion who also liked the warm water and while it never happened to me, one guy did get bit once. They're not as friendly as they look.