Shark-Induced Survival Pressure?

It has often seemed to me that taking a shower temporarily slows or stops menstruation. I haven't found any studies confirming this, though I'm apparently not the only one who thinks it can happen. If it's a real phenomenon, I wonder if it's another sign that humans spent some important period of their development as a species living largely in water. (That hypothesis may be thoroughly debunked by now -- I read about it years ago and haven't checked up on it.) Sharks can smell blood in water from a very long way away. If we did do a lot of prehistoric wading around, women whose menstrual flow stopped upon immersion in water would have had a huge survival advantage.