Would replace some of the existing water tiles, like tiles in flooded piranha room.
This terrain takes twice as long to traverse as regular terrain, unless the player is levitating.
Monsters will not pursue you across deep water if they do not fly, do not blink and are not aquatic (e.g. piranhas)
Swimming in deep water will make items leave your backpack before washing up on shore. My thought is that the item containers prevent this from happening for the stuff they hold inside them.
TLDR: Basically the murky water from Brogue,
I might add this to a mod I'm making. What do folks think of this mechanic?