Putting skeletons and zombies in some water will just drown them. They will make no attempt to swim up unless you hit them.
Mobs dont float next to walls as in: Mob spawner killer
The ocelots can't swim
Mobs not swimming
Chickens can not swim up
Ocelots/Cats don't swim to the surface when underwater and drown unless teleported
Some mobs do not swim up some sink
Mobs can't swim