The website https://www.coldwatersafety.org/contains a lot of great safety related information and covers the topic of cold water thoroughly (I took the themometer image that’s here from that website).

The following is taken from the book “Sea Kayaking Safety“: –

“Cold water is most definitely a dangerous environment and much more commonly encountered [than . If you’re paddling on an icy lake in sub-zero conditions with snow all around then you’ll be only too aware that what’s below you is potentially lethal. Whereas on a warm sunny day it’s all too easy to overlook the dangers of cold water, particularly in late spring when it’s boardshorts weather yet the water temperatures are still really low.

With most potential kayaking hazards, you can see them coming and/or there’s a window of opportunity for taking avoiding action, or getting rescued after things have gone wrong. Whereas falling into cold water without the appropriate clothing immediately puts you in grave danger. Everyone’s heard of hypothermia, but cold water can kill you long before your core body temperature starts to drop to hypothermic levels. This is why it’s so important to understand and respect the cold-water environment.”