Every time you go underwater and then back to the ground you lose your precast matras and all bloodlust stacks.
On some maps like EBG you need to swim quite often or to run across a swamp that gets deep enough in some places to put you underwater.
Especially annoying during a fight, when you might slip from a slope for a fraction of a second into the water or you need to chase someone who’s crossing a lake – if you follow, it cleans all 25 stacks of bloodlust and doesn’t reset mantra cds when you back to the surface, so you can’t precast it again.
It might make sense that you lose bloodlust underwater but it should pop it back when you back.