Jellyfish Lake, Eil Malk Island, Palau, Pacific Ocean

Saltwater crocodiles are native to Palau but there has only been one death attributed to them in recent times and they are generally not considered a threat to divers.
The hydrogen sulfide in the anoxic layer is a serious risk to scuba divers entering this layer. The gas can be absorbed through the skin. In 1977, the maximum safe threshold level for hydrogen sulfide was set at 10 ppm. The concentrations exceed that by eightfold at the bottom of the anoxic layer. However, the hydrogen sulfide concentration down to the chemocline at about 15 metres (49 ft) is reported to be zero, and if the anoxic layer is avoided, the hydrogen sulfide in the lake does not pose a risk for snorkelers.