Jellyfish Lake (Palauan: Ongeim'l Tketau, "Fifth Lake") is a
marine lake 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, between Koror and Peleliu. There are about
70 other marine lakes located throughout the Rock Islands. 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.
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, Mastigias cf. papua etpisoni, and possibly other species in the
lake have evolved to be substantially different from their close relatives
living in the nearby lagoons.
