I'm working on a WIP that focuses on merfolk and takes place entirely underwater. I have a randomly-generated map to help me locate where the land masses/coastlines and such are, but that's only helpful to a point at determining the look of things off the coasts. Stuff like the location of reefs, trenches, volcanic islands, etc. And especially how currents would work. Can anyone help me find resources on that sort of thing so I at least have something to springboard off of?