The only exceptions I can think of were the lakes they dug to get material to build overpasses. They were steep-walled reservoirs, and quite cold. I did a little snorkeling and speargunning without worrying. But, any drainsge ditch was suspect. I remember looking in one around a parking lot. ‘Gator was probably waiting for a cat or dog to take a drink.
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. ?