As we say in England, this is in my opinion 'taking the piss'. It makes a complete mockery of the salaah. Even diving on nitrox with twin tanks in the shallows, a dive will last at the very most one hour, maybe a bit more. He could have easily prayed before starting the dive or right afterward. If it's absolutely necessary, sure; but it just isn't here and I can't think of a situation where it would be.