Anyone rememeber "Goo Lagoon" from Spongebob? The beach where the fish would go swimming?

And everyone used to ask "How can they go swimming in the lagoon if they're already underwater?" It's technically possible. Goo Lagoon was probably a brine pool. Brine is water which contains an exceptionally high concentration of salt, from three to eight times as much as the surrounding seawater, which makes it much more dense. And as such, it sinks to the bottom and does not easily mix with the normal ocean water around it. This can create underwater "lakes" of brine which have distinct surface levels and a sort of "shoreline" where the brine ends and runs back into lower salinity seawater. Submarines have traveled into brine pools and found themselves floating on its surface. So the concept of a body of water where fish could go swimming under the ocean's surface is totally possible.