Brine

Brine is located in the Lost River, and is the pool on the bottom all throughout the biome. It damages the player, causing damage similar to radiation per second. Underneath it, multiple resource deposits can be found containing Nickel, Titanium, and an assortment of other ores. All fauna such as Ghost Rays, Ghost Leviathans, and all flora (except Gel Sacks) are immune to Brine.

Ecosystem
Brine consists of much fauna and roots of what might be trees running through it.

Usefulness
Brine cannot be scanned and doesn't have an exceptional use to the player, only damages it while swimming inside of it or while in the Seamoth. However, within the Brine can be found multiple Large Resource Deposits which contain rare and useful ores which the player can use to make depth modules for the Cyclops and Prawn.

Please add more information if you can, or change the name of what Brine is. I'm not entirely sure that's the actual name.