"Jellyfish Lake is located on Eli Malk island in the Republic of Palau. Twelve thousand years ago these jellyfish became trapped in a natural basin on the island when the ocean receded. With no predators amongst them for thousands of years, they evolved into a new species that lost most of their stinging ability as they no longer had to protect themselves. They are pretty much harmless to humans although some people with very sensitive skin may get a minor sting from them. If you are allergic to jellyfish you should wear a wetsuit or protective clothing."