No jellyfish, sharks, or seaweed! World's largest swimming pool - in San Alfonso del Mar in Algarrobo, Chile - 1013 meters long covers 80 acres, its deepest end reaches and it holds 66 million gallons of water.
"This is Flathead Lake in northwestern Montana, USA. The water is so transparent that it seems that this is a quite shallow lake. In fact, it is feet deep." It's not Flathead Lake unfortunately! It's Avalanche Lake :)