Rescue efforts were called off earlier today in the aftermath of a Costa Concordia shipwreck on rocks off the coast of Italy three days ago. Six of the cruise liner's 4,200 passengers and crewmembers have been reported dead, so far, and another 15 or more remain missing.

As lifeboats filled up and malfunctioned and rescue efforts had yet to arrive on Friday, dozens of passengers took the chance and jumped into the 14-degree Celsius water to swim ashore to the nearby island of Giglio. Was this a wise move?

Chilly water cools the body down much faster than does cold air, but waters warmer than 24 degrees Celsius also can put people at risk for hypothermia, which is why even those missing passengers who might have survived the ship's sinking might have then perished in the water.

For an explanation of how risky it is to be submerged in cold waters—and why even warm water can be dangerous for the body—read: "Hypothermia: How Long Can Someone Survive In Frigid Water?"