Clear Lake is one of the oldest of meromictic marine lakes in Palau and is circa 15,000 - 12,000 years old. It 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 salii and possibly other species in the lake have evolved to be substantially different from their close relatives living in the nearby lagoons.
