I saw a decent sized shark, probably a Tiger, maybe 10ft long right at the end of the runway breakwater at Hickam AFB in Hawaii. Freaked me out as it was only a couple of feet under the surface. I hi-tailed it back around to the shallow cove where we hung out and plopped myself up on the rocks. And no, he didn't seem fazed one bit that I was riding within 10-15 feet of him.
Alligators are evil too, had a friend's ski break down back in the marsh in Charleston with a gator within 50 feet of us. That was the fastest you've ever seen a ski hooked up and towed back to the ramp every, with both of us sitting completely in the trays while I towed.