During the Jurassic period the waters here were shallow and became cut off from the ocean. The area soon dried out, leaving a thick layer of salt and other minerals up to 8km thick. When ocean water returned after the region rifted apart, the super-saline layer at the bottom of the Gulf became an underwater lake. Now brine, which is continually released from a rift in the ocean floor, feeds the lake. David Attenborough narrates.