Short of paddling only in warmer waters, which limits the kayaking season to warmer months, or a visit or move to warmer climates, precautions can be taken to extend the paddling season and minimize the risks of hypothermia.
Wetsuits can be worn which can keep an immersed kayaker functional in 50°F water. Drysuits can extend ones paddling season right up into the months when the water gets "hard". Note that [neoprene hood]?s, [paddling gloves]?, boots, and [insulating layers]? under drytops, along with a good dose of [common sense]? and experience are also needed when paddling in colder waters.
Hypothermia is probably a greater risk to kayakers than drowning. Your core temperature starts to drop, motor skills are impaired greatly if not completely, and cognitive thinking slows. Best practices dictate that you dress for the water temperature not the air temperature. This means that if you are paddling in on a day when the air is 80°F and the water is 40°F you still dress warmly in case of immersion even though you may be uncomfortable. This is the purpose of rotary cooling.
Here is a hypothermia table you can look at to determine how quickly you might lose function if you take an unprotected swim in cold water.
The best defense against hypothermia is staying dry, and if you should flip, getting out of the water as quickly as possible.