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Jellyfish Lake also known as Ongeim’l Tketau (OTM) is one of 50 marine lakes in Palau. These marine lakes, located on different islands throughout the archipelago, are salt water lakes separated from the open ocean. While there may still be ways for water and marine larvae to travel between them, they are isolated enough to have species develop differently in the different lakes.

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Located on Eil Malk Island, one of the Rock Islands, OTM is the only lake open to visitors. The lake gets it nickname, “Jellyfish lake”, from the more than 13 million jellyfish that live in this small inland salt water lake. The majority of these jellyfish are Golden Jellyfish with a smaller number of Moon Jellyfish also being in the lake.

The History of Jellyfish Lake in Palau

There are three small tunnels between the lake and the lagoon. Scientists discovered that about 12,000 years ago at the end of the Ice Age sea levels had risen to a point where these tunnels were no longer above sea level and therefore they flooded and filled the holes on the emerging island creating the lake.

These tunnels still exist today allowing an limited amount of water to be exchanged. The lake is 5.7 ha (14 acres) in size and about 30 meters deep. There is an anoxic layer that extends from about 15 meters (49 ft) below the surface to the bottom of the lake. An anoxic layer is water that has no oxygen. This layer is deadly to divers as the anoxic layer contains high concentrations of ammonia and phosphate, which the human body could absorb through the skin.

What can you expect when you visit Jellyfish Lake?

Expect to find a whole lot of Jellyfish, Golden Jellyfish to be precise. These Golden Jellyfish are a sub-species of the Spotted Jellyfish (Mastigias Papua) and are found in five different marine lakes.

In each of these lakes, the Jellyfish have evolved differently creating five different sub-species. The Golden Jellyfish have a symbiotic algae that lives within their tissues. This algae take sunlight and convert it into a food source which they in turn share with the jellyfish. This represents about 70% of the jellyfish needs with the remainder coming from zooplankton.

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Jellyfish are normally solitary animals but within these marine lakes, they group together. They also follow a pattern that keeps them in the sun. Staying in the sun keeps them away from anemones that are near the shores and if given the chance they will feed on the jellyfish.

The Golden Jellyfish migration pattern in Jellyfish Lake is as follows:

Night - For about 14 hours a day the jellyfish make repeated vertical excursions between the surface and the chemocline in the western basin possibly to acquire nitrogen and other nutrients from near the chemocline for their symbiotic algae.

  • From early morning to about 0930 - The jellyfish move from the center of the western basin to the eastern basin.
  • From early afternoon to about 1530 - The jellyfish move from the eastern basin to near the western end of the lake.
  • As the sun sets - The jellyfish move briefly eastward from the western end of the western basin where they remain through the night

The golden jellyfish rotate counter-clockwise as they swim at the surface, presumably to provide even exposure to the sun for the symbiotic algae in their bodies. Snorkels can swim out and join the Jellyfish.

What Can You Do at Jellyfish Lake?

Snorkeling with the jellyfish is the main attraction of Jellyfish lake. Most dive centers and tour agencies in Palau include a trip to the lake. Visitors must purchase a special permit to visit the lake, however, it can be purchased in conjunction with a Rock Island permit at a discount.

Snorkeling is permitted in Jellyfish lake, but, scuba diving is not. There are two primary reasons for the ban, first is the anoxic layer and second is that the exhaust bubbles from a diver can damage even kill the fragile jellyfish.

Is it safe to swim in Jellyfish Lake?

Jellyfish are known to have swimmers fleeing the water and in extreme cases even closing beaches. These jellyfish are different. The Spotted Jellyfish and the Golden Jellyfish have a very weak sting. Their sting is strong enough to stun their prey. However, most people will not feel a sting from these animals unless it is on very sensitive skin such as around the mouth.

How to Get to Jellyfish Lake in Palau?

To get to Jellyfish Lake, you will need to find a local guide who will take you there. Most of the dive operators in Palau offer half day tours, and a two tank dive as a package as a visit to the lake is usually done in between dives.

Would you like to explore Jellyfish Lake Palau? Feel free to contact us. We have partners that offer dive packages + accommodation and day trips to Jellyfish Lake too.

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Blog written by: Rutger Thole who founded bookyourdive early 2012 because he saw that there was no simple and easy to use platform where divers could go to, to read scuba blogs, browse dive centers within locations and where they could read reviews from other scuba divers.

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