Lynne Cox, probably the most famous and most determined open water swimmer in the world, has a new book with a title that’s as clear as water: Open Water Swimming Manual: An Expert’s Survival Guide for Triathletes and Open Water Swimmers. No, it’s not just her advice, although that alone would be worth the $15.95. As the New York Times reports, Cox consults a range of experts, including marine biologists, meteorologists, hypothermia scientists, emergency medical teams and even the Navy SEALs. What do we learn? Open water swimming dangerous, even for veteran open water swimmers. The Times reports that the exertion can be intense; and swimmers can inhale too much water, lose too much body heat, overheat, underhydrate, become disoriented. Exiting an ocean swim through surf can subject the swimmer to a maddening swirl of currents and bone-breaking beatings from crashing waves. Start with short swims: one to three miles. Always swim with a crew, who makes the decisions about if and when to quit. Be careful what you wear. If swimming near seals or sea lions, don’t wear a black suit, or a predator might mistake you for dinner.