Hey, here's an interesting website from the US Weather Service that talks about what can happen when you fall out of a boat, and into cold water deep enough to be over your head.
Ok, so the water temp is something like 74 right now ........ well, summer is very brief, and it won't be too long before the water temp is down at 34 .... a temp more appropriate for cold water info:
www.weather.gov/safety/coldwater ... click on 'body's reaction to cold water'
I figure the thing to do is to cover your mouth and nose with your hand, and brace yourself for the cold shock .... and maybe slowly count to ten while you keep your mouth and nose covered ........ and be wearing a pfd .... or, a home made noodle swimmer's belt ....which do indeed work very good for swimming with its body center, balanced buoyancy ....... something that a pfd does not have.