Lots of nurse sharks and stingrays out at Shark Ray Alley in Ambergris Caye, Belize. Course, that's because they know that there's food there. Snorkeling only, no scuba allowed. The water is about 6 feet deep where the boats anchor.
My experience went something like this:
Rene the guide -- I could hear him up in the boat while I was floating around and looking down into the water:
"That's it Matt, when the shark comes up to you just make the your fingers into a fist and then they will not think you have food, so they will swim away. See how tame they are?"
They were just swimming right up to us, and they'd bump into you and then brush by and you could run your fingers down their back or belly and they'd keep going.
More from Rene:
"Okay Matt, here comes a good looking one, we will get him over here with some sardines. Here he is. Yes, make the fist like before. Wait, no, not like that, you want to tuck your thumb in. Oh...oh...oh no...come here, we will put some hydrogen peroxide on that..."
*sigh*, Matt's first shark bite ever. Not bad, mostly healed up now. Looked like I put my thumb in a cheese grater, though
One must always remember that no matter how nice and friendly these animals seem, and no matter how many stories you hear about hugging the "nursies", THEY'RE STILL SHARKS!!!!
Matt