Jellyfish Lake

golden jellyfish

Jellyfish Lake is located on Eil Malk island in Palau. Eil Malk is part of the Rock Islands, a group of small, rocky, mostly uninhabited islands in Palau’s Southern Lagoon. Jellyfish Lake is one of Palau’s most famous dive (snorkeling only) sites. It is notable for the millions of golden jellyfish which migrate horizontally across the lake daily.

The jellyfish found in the lake have stinging cells,  but are not in general powerful enough to cause harm to humans. It has been reported that it is possible to notice the stings on sensitive areas like the area around the mouth.

Jellyfish Lake is connected to the ocean through fissures and tunnels in the limestone of ancient Miocene reef. However the lake is sufficiently isolated and the conditions are different enough that the diversity of species in the lake is greatly reduced from the nearby lagoon. The golden jellyfish and possibly other species in the lake have evolved to be substantially different from their close relatives living in the nearby lagoons.

The oxygen concentration in the lake declines from about 5 ppm at the surface to zero at 50 feet (15 m). The top ten feet (3 m) of the anoxic (oxygenless) layer contain a dense population of bacteria, at least one species of which is a purple photosynthetic sulfur bacterium. This bacterial layer absorbs all sunlight so that the anoxic water below the bacterial plate is dark, but transparent. The visibility is estimated to be about 100 feet (30 m).

The anoxic layer contains a high concentration of hydrogen sulfide, and is potentially dangerous for divers, who can be poisoned through their skin. This risk is mitigated as scuba diving equipment is not allowed in the lake, thus limiting the depths to which individuals may dive.

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