money
Like the old joke goes: "the only way to make a small fortune in scuba diving is to start with a large fortune." Lots of people earn a living with scuba diving, but very few become rich.
Being squished by the water pressure, running out of air, getting trapped underwater, getting raped by a crab and in genral death
people can run out of air or drown
S.C.U.B.A. stands for Self Contained Underwater Breathing Apparatus