The temperature was a hair above 40 degrees late in March when Darren Miller, wearing only a Speedo and a smile, plunged into the frigid waters of Keystone Lake in Westmoreland County. Mr. Miller, 27, of Delmont, swam for only a few minutes, partly because he was posing for news cameras, partly because he'd be endangering his life if he swam for much longer. "Anything over 20-30 minutes, you can get hypothermia," he said. During a typical workout when temperatures are warmer, Mr. Miller will swim the one kilometer length of Keystone Lake dozens of times.