That's interesting. I'd have thought a water body like that would stratify from mid spring through mid fall in FL. Cold under 10-15 ft. down, by summer, but very warm above the thermocline. ?
Florida. Who can remember what month it was? The connecting canals were warm enough. I recall going through a culvert which was deep enough for fish, so it may have been the rainy season...summer/fall. South Florida could get torrential rain, daily. Warmer water may have drained off. The water got creepy dark and chilly really fast. No shallows. They were apparently “ mined” for the coral used to build the overpasses. You could find two of them for every overpass around Homestead. They were dug from equipment on floating platforms. A diving friend found a piece of excavating equipment on its side at the bottom of one of them. Also a Mason jar with some bones and beads in it. Probably from the Haitian population.