Beavers said the search will resume Sunday afternoon.
The man, whose name has not been released, was with a group of people who rented a boat Friday and were about 300 yards off shore around 3:25 p.m. when a man jumped into the lake to cool off. When he began struggling in the choppy waters, the Alhambra man jumped into the water to help him and also began struggling, she said.
A third man then jumped in to help both men. The first and third men made it back to the boat, but the second man went under, Beavers told the San Gabriel Valley Tribune.
Divers from the sheriff's department searched until about 7 p.m. Friday.