The extremely cold Colorado River water is one of the prime reasons for Grand Canyon’s life jacket regulation. Simply, if you are on your boat and it is not tied to the shore you will wear a properly fitted life jacket 100% of the time.
At 47 degrees even in flat water you have about 5 to 10 minutes of muscle activity to rescue yourself. In ten minutes your muscles stop working and your chances of rescue are very poor. Updated 2011.
