Jellyfish Lake

Jellyfish Lake
Ongeim'l Tketau (Palauan)
Aerial view, looking west
Jellyfish Lake is located in Palau
Jellyfish Lake
Jellyfish Lake
LocationEil Malk, Rock Islands, Palau
Coordinates7°09′40″N 134°22′34″E / 7.16111°N 134.37611°E / 7.16111; 134.37611
TypeMeromictic
Basin countriesPalau
Max. length460 m (1,510 ft)
Max. width160 m (520 ft)
Surface area5.7 ha (14 acres)
Average depth30 m (100 ft)
Water volume1.71 million m3 (60 million cu ft)
Surface elevationSea level
FrozenNever
IslandsNone

Jellyfish Lake (Palauan: Ongeim'l Tketau, lit.'Fifth Lake') is a marine lake located on Eil Malk island in Palau. Eil Malk is a part of the Rock Islands, a group of small, rocky, mostly uninhabited islands in Palau's Southern Lagoon, between Koror and Peleliu. There are about 70 other marine lakes located throughout the Rock Islands. Millions of golden jellyfish migrate horizontally across the lake daily.

Jellyfish Lake is connected to the ocean through fissures and tunnels in the limestone of an 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, Mastigias papua etpisoni, and possibly other species in the lake, have evolved to be substantially different from their close relatives living in the nearby lagoons.