This is from an interview with legendary stuntperson, Dick Warlock.
It was a round tank. Stephen Spielberg is over here, looking through a porthole. You got the cage here. You got the Bruce* facing this way. Over her, you got Whitey Crumb, who’s using one of these gadgets that you use to fly an airplane with to move the shark. Stephen’s over here talking to Whitey on the microphone. “Move the shark.” They’re doing all that stuff. They send the shark in. It busts through the cage, hits me in the stomach, knocked my regulator out of my mouth, scratched me around. I’m trying to get the regulator. I’m trying to signal Freddie Zendar, who’s the stunt coordinator. I’m drowning out here! Get me out! I finally get the regulator back in my mouth and we finish that day. And go on with it and on with it and on with it for a week. But I almost bought the farm that time, well, might not have died, someone would have rescued me. So that’s that story. I’ve had a lot of things come close.
*Fun Fact: Bruce is the name given to the animatronic sharks used in the film Jaws. You may recognize this nod to Jaws in the film Finding Nemo.