Although beautiful to look at, Southern California beaches are "cold" for swimming, without a wetsuit. The beaches in South Florida are much warmer than the beaches in SoCal. Hawaiian beaches are very warm and comfortable. For Southern California, I recommend swimming in swimming pools and lakes. SoCal ocean water temperature doesn't change that much between Summer and Winter. Most of the people in the SoCal ocean waters are kids and surfers. Most people just lay on the beach or play volleyball on the sand in the Summer and leave the ocean swimming to the hardy souls.