How is their existence even physically possible? https://lolstatic-a.akamaihd.net/frontpage/apps/prod/universe-map/en_US/85d98a83e3366884d6ac968ce7034cda708f686f/assets/src/assets/images/slides/bilgewater_thecity_02.jpg
beneath that PoV there's a really really big shop vac pulling that water out of the hole.
In a less nonsensical way this could be inspired by spillways in dams.
there's probably a big ass hole that goes out to the other side of the world so all the water that falls in goes into the ocean on the other side... duh [slayer-pantheon-thumbs]
Questioning water falls when we have 
time manipulation and 
being a thing
Lets call it Nagakaiborous falls :-)
I blame the Mother Serpent.
You ever played Final Fantasy 12? The Ridorana Cataract is pretty much the same thing except far larger, it spans the distance the eye can see. But in worlds of magic, these things aren't exactly held to our own logic.
Have you ever been to the Panama Canal? Or have you seen any canal? The sea on one side of Biglewater is higher than the sea on the other side... I'll be it, to a fanciful extreme.
