Santa Cruz, CA every 4th July sponsors a Pier to Pier swim. Starts at Capitola wharf, an open water swim 6 miles ends at Santa Cruz. Ocean water swimming is not easy. I knew a gal (in her 30's) many years ago who swam the race every year. I use to swim laps to stay in shape during winter months. She trained at same pool, she'd swim laps for 30 mins per session. Not an ounce of fat on her body