Ideas for fully underwater plots?

Ok so I’m running a fully home brew underwater campaign. All species open to the players. Some are playing classic water breathing races, some are playing people with blessings or magic to breath underwater, some cannot breathe underwater at all but wear suits.

I have a main overarching story and mechanics figured out, but I’m having a hard time finding random encounters that take place solely underwater that aren’t meant for above ground parties, aren’t just coastal, or are amphibious (there’s no land in my world)

If anyone has any resources or ideas that would be great. This could be hooks, maps, websites, personal experience, etc.

For reference this is a party of 4 level 3 characters in the first few sessions of the game: we have a rogue, cleric, monk, and a fighter.