This is an underwater river in Mexico.
The river is made of hydrogen sulfide. As hydrogen sulfide is much denser than water, it stays at the bottom and creates its own river. However, hydrogen sulfide is classified as a level 4 in the MSDS, and is very dangerous. Definitely not something you want to go take a dip in.
OH! That’s why there’s water in Bikini Bottom!
Submitted by rainbowbonkers