My wife Louisa is an open-water swimmer. Her idea of a good time is to don her thin (1/8 inch) wetsuit, slide into Humboldt Bay off the C Street dock, and swim around for a good 30 minutes. Maybe 50 minutes in summer, when the water is warmer. My job, as her "spotter," is to accompany her when she wants to swim across the channel, over to Woodley or Indian Island -- it's tough for the crew of a boat to see a head in the water, whereas in my kayak, I'm harder to miss. Plus I can keep my eyes and ears out for her -- down there in the water with her ears covered by two bathing caps, it's unsafe for her to be in the channel on her own.

The question she's always asked is, of course, "How cold is it?" December water temperatures in the bay hover around 50 degrees F (10 degrees Celsius), while last summer, it got up to a balmy 62 degrees. Her wetsuit keeps her torso warm -- the water trapped between the suit and her body warms up during the first minute or so that she's in, so she mostly feels the cold on her unprotected legs and arms. Neoprene gloves and wetsocks help keep her hands and feet comfortable, and she avoids dunking her head in, both for warmth and potential hygiene considerations.

So how cold could the water be and still allow someone to swim? First, let's look at an extreme example: open-water long-distance swimmer Lynne Cox, author of Swimming to Antarctica. She's best known for her 1987 two-mile swim in the Bering Strait between the United States and the then Soviet Union in 1987, when the water temperature between Little Diomede Island (Alaska) and Big Diomede Island (Russia) averaged around 40 degrees F. She's also swum over a mile in the freezing waters of Antarctica, clad only in a swimsuit, cap and goggles. She's exceptional, of course -- and has been cold-water swimming since age eight.

OK, so that's Lynne Cox -- how about you or me? According to the U.S. Search and Rescue Task Force, we regular folks can expect exhaustion or unconsciousness in 50-60 degree water in 1-2 hours, and death in 1-6 hours, depending on many factors, including what you're wearing, your body fat and your psychological endurance. In water between 40 and 50 degrees, those figures drop to 30-60 minutes for exhaustion/unconsciousness and 1-3 hours death.

So what should you do if you happen to find yourself unexpectedly in cold water? Get out! Cold water robs body heat 32 times faster than cold air at the same temperature.

And then there's Louisa. Her follow-up to a cold dip in the bay is to jump into our hot tub, which at 105 degrees is, she assures me, better than dessert. I'll take her word on that, not feeling the necessity to check it out for myself -- you think I'm crazy?

Barry Evans ([email protected]) is a recovering civil engineer living in beautiful Old Town Eureka. His book "Everyday Wonders: Encounters with the Astonishing World around Us" led to a four-year stint as a science commentator on National Public Radio.

CAPTION: Not Lynne Cox! Louisa in the bay. Photo by author.