Underwater combat needs an overhaul.
If an opponent is killed underwater he shouldnt be able to swim faster and further than what he could when he was alive! If you are killed underwater, there should be no movement allowed(save for up) and if you reach the top of the water, you should not be able to re-submerge and abuse invulnerability coding.
Water combat is fun, right up until the point where you kill someone and know it will take 2 minutes to down them.