Out of Your Depth Achievement
Out of Your Depth5
You're gonna need a bigger boat...
At any time during your playthrough, make your way to the beach in Western Los Santos and hop into a jet ski near the pier. Drive out into the ocean until the water is dark blue, as this is where you can generally find sharks if you wait long enough (you will know if a shark is nearby when there is a red dot on your mini-map). Once a shark appears, hop off your jet ski and dive underwater. The shark will ignore you at first, but once it gets close it will finally eat you and the achievement will unlock.