The best case scenario for Cold Water Immersion is to "reduce or prevent the risk". If you're boating in cold water, it's as simple as making sure not to overload your boat, avoiding situations where you may fall overboard and, of course, making sure that everyone is wearing a Canadian approved lifejacket to protect in the case of an unforeseeable emergency.
The best choice in flotation equipment for Cold Water Immersion is a type that will offer the maximum thermal protection such as a floater jacket and pants or a one-piece survival suit. If you do find yourself in cold water, in addition to having proper flotation, there are some things you can do to delay the onset of Hypothermia. Drawing your legs up close to your chest and wrapping your arms around them in a tuck position will help conserve body heat. If you're in a group, huddling together as close as possible will also help conserve body heat.
Without thermal protection you can lose body heat 25 times faster in water than in air with similar temperatures and that can be increased by a factor of up to 10 with movement like swimming or moving water.