Water aware monsters is a modification for Quake made by Kyle R. Hofmann. This modification is intended to make it so Monsters can swim in Water and will drown in a similar manner to the player. They also are intended to have the intelligence to attempt to surface before they start to run out of air.
Note that this modification, as is standard with Kyle R. Hofmann modifications, is provided as a .DIF file. There is a lack of closure, "};", on water_checks before the code attempts to void WaterMove. monster_drown_check similarly lacks a ";". If these changes are made, the game can be loaded normally, but the modification changes do not appear to function. This likely has to do with the fact that while a "monster_drown_check" exists, it is not used outside of a float function in monsters.qc, therefore there is no defined manner in which this function is being called.