Located on an uninhabited rock island off the coast of Koror in Palau, Jellyfish Lake is a saltwater lake that was once connected to the ocean, but is now cut off.  The isolated lake became the perfect setting for a jellyfish explosion!  Marine biologists speculate the jellyfish were trapped in the lake 12,000 years ago after a rise in sea levels post-Ice Age. The jellyfish evolved to have almost no stingers, because they have no natural predators present.