Jellyfish Lake is a salt-water lake located on Eil Malk which is one of the limestone islands that make up the Rock Islands in Palau. This spot is one of the most popular stops for the travelling SCUBA diver who visits the Micronesia area. Oddly enough, and for reasons that will soon become apparent, no one SCUBA dives there.
The primary attraction at Jellyfish Lake are its inhabitants. The lake is populated by jellyfish (Golden Mastigias and Moon Aurelia), Cardinalfish and various anemones. The golden mastigias jellyfish that are found outside of Jellyfish Lake bear nematocysts that will light up your tender flesh like a christmas tree. The mastigias in Jellyfish Lake, however, have been isolated in this lake for so long without predator or prey that the stingy goodness of the nematocysts is no longer necessary for their survival. That's just a theory, of course. It's not my theory but I like it. While the mastigias have lost most of their sting, some have a little punch left and some folks have reported mild irriation to sensitive skin areas such as the face. On my visit, I had no such experience. The aurelia have little to no sting, here or elsewhere, and apparently do not require or welcome the zooxanthelae. Not being bound to the sun and still a predator, the aurelia are mostly nighttime denizens.
The mastigias have teamed up with a symbiotic, photosynthetic algae (zooxanthelae - not uncommonly found cohabitating with some corals) to supplement their diet. During the day, the mastigias migrate from one side of the lake to the other, following the sun as it passes overhead and shines over the hills that surround the lake. At night, the mastigias descend to a depth of approximately 15 to 18 meters where the water transitions from the brackish shallows to an oxygen-starved layer rich in poisonous hydrogen sulfide. Something here seems to make the zooxanthelae happy and productive.
The sight of the swarm of thousands upon thousands of golden mastigias drifting slowly through the sunlit shallows of the lake is an experience trumped only by the experience of drifting along with them. Overcoming the ingrained reflex of backing slowly away from a swarm of large, brightly colored jellyfish, which every SCUBA diver worth his sea salt has acquired, is difficult. The sheer alien nature of the experience; the caress of the firm bells and the feathery tendrils hints that you may have found the gates of R'yleh or be aloft amongst the spheres of Yog-Sothoth.
This is why you have travelled thousands of miles.
This is why you have spent thousands of dollars.
This is why you have come.
This is some freaky, cool-ass shit.
Jellyfish Lake is one of at least two others with non-stinging mastigias in the Rock Islands, but to my knowledge, they are unique oustide of Palau. Concern regarding the effect of exhalation bubbles on the jellyfish and the dangers of contact poisoning from the hydrogen sulfide in solution in the lower layer of water are the primary reasons for the prohibition against SCUBA diving in Jellyfish lake. You are encouraged to not handle the jellyfish or disturb them too roughly with your fins. Eil Malk can be reached by boat from Koror, the nearest Palauan island with an airport. If you are in the area, don't you dare miss it.
The coordinates for the dock on Eil Malk
07° 10.320 N - 134° 22.899 E