Freediver Jake Koehler, better known as DALLMYD, ignored posted alligator warnings to explore what looked like a garden variety Florida swamp. Below the duckweed covering the surface, he found a crystal-clear freshwater spring.
Bonus video: underwater metal detecting for river treasure:
• Found Secret Swimming Hole Underneath a Nasty Florida Swamp! – Freediving (Beware of Alligators) (YouTube / DALLMYD)