The weekend before Hurricane Katrina hit NOLA we were ~75 mile south of Venice in about 5300' of water. Greasy calm, hotter than hell. Only breeze was when we were running. About 1pm we decided to jump in and try to cool off. I dove off the tuna tower and went down about 25' thinking I'd hit a little cooler water - surface temp was in the mid 90's. Temp never changed. Floated around for about 10 minutes but the water was not even comfortable. No dive ladder on the boat so we had to step on the foot of the motor to drag ourselves out. I was the last guy to come out. Just as I was starting to pull myself out of the water the other guys start screaming for me to get my ass in the boat! I pulled up and looked back to see the biggest tiger shark I've ever seen (I've seen some giants) go right under where I'd been. Her dorsal fin hit the motor well - that's how shallow she was! I don't think she was there to eat - or one of us would have been dead long before we saw her - think she was just curious and checking us out. Got my attention though for sure! It made one more pass before leaving - it had to be 14-15' long! We pitched a 40# YFT on a 130 we had rigged for shark and she swam right past it and didn't give it a 2nd look.