According to the video’s description Jellyfish Lake, located on Eli Malk island in the Republic of Palau, is home to thousands of (mostly) stingless jellyfish that were trapped there thousands of years ago in a natural basin. They are harmless to human beings and have a symbiotic relationship with algae living in their translucent guts. At night they descend to the depths of the lake to feed, and during the day ascend to the surface following the track of the sun. The algae in their systems convert the sunlight into sugar for the jellyfish.
