Do Waterproof Calorie/Heart-Rate Monitors Exist?

I'm hoping for some recommendations because I have no idea what I'm looking for. I've never owned a heart-rate monitor before but I'm looking at buying one to more accurately count calories expended since MFP supposedly over-estimates. I do some gym work once or twice a week, but mostly I love to SWIM. I swim for 30-60 minutes and then follow it up with a water aerobics class at the local pool. Therefore, if I buy a monitor, it has to be waterproof.

Anybody have any suggestions? I am completely lost. I see 'water resistant' but that worries me and reviews are here or there.