Diane Walton clearly remembers the first time she plunged into the frigid waters of the San Francisco Bay, almost 20 years ago. “It was so cold that I thought my organs might explode!” the 73-year-old says, her long, grey hair streaming behind her as we sit on a wooden jetty basking in the bright, mid-morning Californian sunshine. One of the local sea lions strung out along the sand barks a laugh as if in response.
Today, the water lapping at our ankles is a brisk 12.7C. But you wouldn’t know it from watching the swimmers around us, who are snapping on
