Jellyfish Lake - tropical pond with safe jellyfish


Medusa Lake - a small lake, a highlight of the Rocky Islands archipelago (Rock Islands) in Palau. At first glance, it’s the most ordinary lake, but it is worth diving under water, a person falls into another world, a world of royal peace, tranquility, it seems that nature is engaged in meditation.

Lake Medus is located in the eastern part of the island of Malk Malk. This is a relatively small lake, the size of which is 460 by 160 meters. The water in the reservoir is brackish, which is quite natural, because the lake is separated from the ocean by a small strip of land, only 200 meters. The depth of the lake is 50 meters, but this turned out to be enough to create an amazing world that attracts divers from all over the world - the kingdom of jellyfish.

The uniqueness of the lake

More than 15 thousand years ago, as a result of tectonic shifts, coral reefs began to gradually rise from the bottom, forming bizarre coral labyrinths above the surface of the water. At the same time, the collapse of a large rock occurred, the stone blocks of which fell into the water, cutting off part of the ocean. Thus, more than 70 small lakes were formed, separated by small land areas. Several jellyfish were in these new bodies of water. Since the jellyfish did not have enemies in them, their number grew; in the process of evolution, the inhabitants of these waters lost stinging cells and became completely harmless. This fact attracts a huge number of tourists who want to "chat" with jellyfish in depth.

It is believed that the total number of jellyfish living in this unusual lake reaches two million individuals. The number of jellyfish is so great that their mass can be easily seen even while on the plane. However, only two species of jellyfish inhabit this lake - the golden (Mastigias papua) and the lunar (Aurelia sp.) Jellyfish. Golden jellyfish has a huge numerical superiority over the moon. There are other differences in the structure of the body of golden jellyfish due to which some biologists propose to separate these jellyfish into a separate subspecies. Golden jellyfish is a transparent gelatinous body with a golden hue, on the edges of which are small tentacles.

These jellyfish do not reach large sizes. Their maximum size is equal to a soccer ball, and the minimum - to a cherry.

The water in Lake Medusa is divided into two layers: the upper layer and the lower. The top layer of water contains much more oxygen than the bottom and at a depth of 15 meters the air content is almost zero, and the most interesting is that the top layer of water never mixes with the bottom. A small influx of fresh water is provided to the upper layer of water through the tunnels connecting the lake with the ocean. The water of the lower layer is saturated with hydrogen sulfide, phosphates and ammonia, in which only a few types of bacteria can survive. For divers, it is undesirable to be in the lower layer, because if you do not have a special underwater wetsuit, then through the skin you can get very serious poisoning.

Since jellyfish need oxygen, they try to live in the upper layer of water, but this does not prevent them from making frequent migrations every day, both horizontally and vertically, often descending to the border of the oxygen-free layer of water. It is safe to say that migrations of golden jellyfish are carried out with special organization and rhythm. Jellyfish all night and until noon, rise and fall in the upper layer of water, to absorb nutrients from it. When morning comes, they move from the western part of the lake to its eastern part, and after lunch they again gather in the western side of the lake. Floating at the surface of the water, jellyfish rotate counterclockwise, which provides excellent illumination to the symbiotic algae living in their body, and algae, through photosynthesis, turn the energy of the sun into sugar, which subsequently feeds on jellyfish.

Lunar jellyfish move in the same way as golden jellyfish, but not in such an organized manner, although it can be said that their ripple along the lake is also massive. At night, moon jellyfish catch copepods located near the surface of the water, which make up most of their diet in the lake.

Some biologists have suggested that the migration of jellyfish between the eastern and western parts of the lake is associated with anemones Entacmaea medusivora, which feed on jellyfish. These sea anemones live off the eastern shore of the lake. Jellyfish try to avoid shade and stay in the light. Following the most illuminated area, they are better able to avoid encounters with anemone dangerous to them.

In 1998, Lake Medusa almost completely lost its main inhabitants - golden jellyfish. By December 1998, their numbers in the lake had fallen to almost zero. It is believed that such a sharp decrease in the population was due to the influence of the powerful phase of the El Niño phenomenon, during which a redistribution of the enormous masses of warm water near the surface layer of the ocean occurs.

As a result of El Nino, the temperature of the water in the lake rose significantly, which killed the symbiotic algae, without which the jellyfish can not survive. In 1999, they could not find a single golden jellyfish in the lake, but in January 2000 they began to appear again, and today their numbers have completely recovered.

Picturesque clusters of jellyfish attract a lot of tourists and scuba diving enthusiasts to the lake. Swimming among lake jellyfish is quite safe, as they have almost completely lost the ability to “bite”. Nevertheless, people with sensitive skin or allergies are advised to use protective suits when immersed. Diving jellyfish in the lake is allowed only with a mask and snorkel, and scuba diving is prohibited.

Scuba gears are prohibited for two reasons: firstly, air bubbles from the scuba gear fall under the dome of the jellyfish, why they can die, and secondly, the scuba gear allows a person to dive to a depth of more than 15 meters, where the oxygen-free layer is.

Mass immersion in the lower layer of the lake will necessarily cause mixing of the upper and lower layers of water (which never happens under natural conditions), and the entire ecosystem of the lake will be irrevocably damaged, which is fraught with death for all its inhabitants. In addition, a careless diver may himself receive fatal poisoning through the skin, while in the lower layer of water saturated with hydrogen sulfide and ammonia.

Of all the inhabitants of the lake, only combed crocodiles can be a real danger to tourists. But they themselves prefer to stay away from people, and for all the time only one attack was recorded, which ended in death.

Medusa Lake

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Lake Medusa, or Ongeim’l tketau, in the Rocky Islands archipelago (Palau) is located in the east of the island of Eil Malk, more than 20 km southeast of Koror.

Lake Medusa is one of eight lakes in Palau that contain large populations of golden jellyfish, moon jellyfish, or both. However, with the exception, all others are closed to tourism under the State Mountain Islands Conservation Act Koror.

The dimensions of the lake are 460 m by 160 m, the mirror area is 0.057 km². The lake is a meromictic, slightly saline reservoir, separated from the ocean by a strip of land of about 200 m. Its depth is up to 50 m.

12000 to 15000 years ago, one limestone rock of the islands of the nation of Palau cut off the island from the ocean, and as a result a sea lake was formed. Several jellyfish were closed from the inside. Since there were practically no predators, they began to multiply and develop. Today, more than 10 million jellyfish live in this amazing lake. Their burning hairs have become evolutionarily useless since there was no one to defend against, and were lost over time, now swimming with jellyfish in the jellyfish lake is absolutely safe.

Unfortunately, the population of jellyfish almost died as a result of the environmental disaster of 1998 - 1999. The water temperature in the lake rose so much that the zooxanthellae symbiotic algae could not survive. This circumstance probably led to the death of almost the entire population. However, by the beginning of 2000, the number of jellyfish rose again to its previous level.

Scuba diving in the Medusa Lake is prohibited due to the fact that in the lower layer of the lake, at the very bottom, is hydrogen sulfide, which has a negative effect on the human body.


Jellyfish Lake in the Palau Archipelago (Jellyfish Lake).

Palau is a magnificent archipelago of the Pacific Islands. It consists of about 300 small islands and 3 larger ones. The archipelago is washed by the Philippine Sea - the largest and deepest sea in the world.

Inside the archipelago is a unique in nature lake of jellyfish, which is home to several million of these beautiful creatures.

Due to the toxicity of water at a depth of more than 10 m, scuba diving is not possible here. And the jellyfish that live in this lake are not dangerous for people and cannot sting. When a person jumps into the water, they simply part in front of him and form a unique picture.

It was because of the toxicity of this water that it was impossible to grow and develop here for other organisms, but for the reproduction of jellyfish these are ideal conditions.

Wiki: en: Lake Medusa

  • en: Jellyfish Lake
  • de: Ongeim'l Tketau
  • es: Lago de las Medusas

    This is a description of the attractions of Lake Medusa 970.8 km east of Davao Del Norta, (Palau). As well as photos, reviews and a map of the surroundings. Find out the history, coordinates, where it is and how to get there. Check out other places on our interactive map, get more detailed information. Get to know the world better.

    Lake features

    The greenish lake is small in size. It has a length of 460 m, a width of 160 m and covers an area of ​​slightly less than 6 ha. A strip of land two hundred meters wide separates the land from the ocean.

    The lake appeared 10-12 thousand years ago, after two tectonic plates collided, and a hollow formed. Salt ocean water began to seep through the holes in the rock, and jellyfish appeared in the new body of water along with the water. However, the passages through which water flowed were small, and larger predatory fish did not enter the isolated lake.

    The reservoir has a depth of up to 50 m. It is filled with water, the salinity of which is 28 - 32 ‰. The water in the lake is divided into two levels. In the upper layer, where there is a lot of oxygen, all its inhabitants live. Through the three tunnels connecting the reservoir with the oceans, during the tides, fresh water constantly flows into it.

    The lower layer begins at a depth of 15 m and reaches the bottom. A large amount of ammonia, phosphate and hydrogen sulfide is dissolved here. There is practically no oxygen at the bottom, so the lower part of the lake is unsuitable for life. It is curious that both layers of water are isolated from each other and never mix.

    What jellyfish live in the lake

    In the open ocean and seas, jellyfish feed on tuna, sea turtles, moon fish, salmon and some birds. The body of jellyfish consists almost entirely of water, and they do not represent special nutritional value. Animals eat jellyfish only when they lack other foods. In a closed lake in Palau, jellyfish do not have natural enemies, so they actively reproduce.

    In an unusual reservoir there are two types of jellyfish - eared (Aureliaaurita) and gold (Mastigiaspapua). Interestingly, the population of eared jellyfish, which is also called ordinary or lunar, is huge. They are found all over the planet, and especially many eared jellyfish in the waters of the temperate and tropical zones, in the Black and Mediterranean Seas. This species of jellyfish has spread widely around the world, as it is able to withstand significant fluctuations in temperature and salinity of the water.

    Why are local jellyfish safe

    Almost all jellyfish living on Earth are dangerous to humans. Their stinging cells cause inflammation on the skin, similar to nettle burns, and bites of some species even lead to death.

    Lake Medusa in Palau is the only place in the world where tourists can safely swim surrounded by a large concentration of jellyfish and not be afraid for their own health. This became possible because the local jellyfish lived in an autonomous environment for a long time, and their biology has changed greatly.

    Ordinary jellyfish are not vegetarians. With their moving tentacles, they grab plankton, crustaceans, insect larvae and small fry. There is very little animal food in Lake Medusa, and in order not to die of starvation, the jellyfish cut off from the World Ocean had to switch to a different type of food and begin to lead a vegetarian life. In the process of evolution, the stinging cells covering their tentacles have died out. Therefore, swimmers in the lake swim calmly - “burns” do not threaten them.

    Both types of jellyfish learned to coexist with symbiotic algae - zooxanthellae, thanks to which they produce a significant part of the necessary nutrients. Seaweed also does not remain in the loser. They inhabit the translucent tissues of jellyfish and exist due to their metabolism.

    Jellyfish migrations

    Each of the species living in the lake has its own strategy for moving along the reservoir. Golden jellyfish make rhythmic horizontal and vertical movements. Mass migrations of hundreds of thousands of individuals occur strictly at a certain time, and the “dance” of a huge number of jellyfish does not leave indifferent any tourist!

    At night and until 2 p.m., golden jellyfish, like floats, move vertically along the surface of the water. Rising and falling, they absorb useful substances from the lake. When the sun begins to illuminate the pond, these jellyfish begin a plan of horizontal migration. Until 15.30 they cross from the eastern part of the reservoir to the western, and then return to the place of overnight.

    Floating near the surface of the water, golden jellyfish rotate counterclockwise. Such movements allow them to achieve uniform illumination of all parts of the body, and the algae living on them receive all the necessary conditions for photosynthesis.

    Long-eared jellyfish behave differently. At night, they float closer to the surface to catch prey. These jellyfish feed mainly on copepods, which in the dark prefer to swim in the upper water level.

    Jellyfish swimming

    On the island where the unique lake is located, there are a dozen more smaller reservoirs inhabited by jellyfish. However, snorkeling for tourists is allowed only in Lake Medusa. Swimming in this pond requires certain safety precautions from divers. All travelers must be warned that at a depth of over 15 m, many trace elements harmful to humans have been dissolved in water. Poisoning through exposed skin occurs very quickly and can cause severe intoxication of the body, so diving is prohibited here.

    In addition, scuba diving is not permitted in Lake Medusa. Air bubbles that form during scuba diver’s breathing fall under the dome of the jellyfish and can lead to its death. For these reasons, they swim in the lake only in the upper layer of water, using fins and a mask. Guides carry those travelers who do not know how to swim on the lake on foam mats, so that they also have the opportunity to look at the accumulation of jellyfish from an arm's reach.

    A convenient wooden pier has been built for divers near Lake Medusa. Here they change clothes, relax and leave their things before diving.

    With a massive accumulation of jellyfish, it is impossible to avoid contact with them. However, all travelers who have visited the lake note that contact with animals does not leave unpleasant impressions. On the contrary, during a meeting with soft and translucent bodies, all swimmers receive only positive emotions.

    Travel Tips

    • For permission to visit a natural attraction or permit you need to pay about $ 100.
    • An hour is enough for swimming among jellyfish.
    • Least of all people near the lake in the afternoon.
    • Travelers who come here are forbidden to use sunscreens, because they pollute the natural reservoir and can damage the jellyfish living there. In order not to sunbathe, you should take care of long-sleeved clothing or wear neoprene suits for swimming.
    • The weather on the island is hot, so a supply of drinking water is not out of place.
    • Boats with tourists moor to the other side of the island. From here to the lake you need to make a short path through the jungle. About three minutes takes a steep climb and the same amount of time down to the pond along the trail. It should be borne in mind that after a rain the rocky path becomes slippery, so travelers are advised to shoe in sturdy comfortable shoes and be careful not to slip and fall.
    • The water in the lake is unclear, and visibility reaches only 5 m.
    • The most spectacular pictures of jellyfish are obtained in sunny weather.

    How to get there

    From Russia, the Republic of Palau is reached via Japan, the Philippines, South Korea, Taiwan, or Guam. Lake Medusa is located in the middle of the Palau Archipelago. It lies in the east of the uninhabited coral island of Ayl-Malk.

    Traveling to a unique reservoir is included in many tours of the Palau Islands. You can buy such a tour at any travel agency in the largest city of Palau - Koror. If you wish, you can easily hire a boat to Ail-Max here. The road to the island takes 40-45 minutes.