The victim, who was from Chula Vista, had rented a jet ski and was on the lake on the Fresno County side when witnesses heard screams coming from the water just before 2 p.m.
A visitor to the lake in a day-use boat headed over immediately, found him in the water next to his jet ski, and pulled him onto the boat.
The victim was unconscious and not breathing. Authorities believe he was under water for 20-30 minutes.
The rescuers performed CPR on him, and he was rushed to a hospital, where he was later declared dead.
The visitors on the boat also rescued a female victim, who had minor injuries.
This incident comes after a 15-year-old boy from Fresno died after being pulled from the water at Millerton Lake on the Madera County side last weekend.
A day after that incident, a 46-year-old man died after being found unresponsive in the wave pool of Fresno's Island Water Park.
First responders are urging everyone to take safety precautions when heading to any local pool or waterway.
This story is developing and will be updated.