When mobs (passive or hostile) are spawned one block beneath the surface of the water they do not swim upwards. This may also happen when they are pushed one block or more below the surface.
MC-36543
Mobs not swimming
Resolved
Duplicate
0
ApeRover
(Unassigned)
Unconfirmed
mob
Minecraft 1.7
Retrieved
There is downwards flowing water under the source blocks.