Any water temp below 50 degrees can shock your systems so that you do not even know how to breath NEVERMIND find which way is up. Especially if you are not expecting it, and anyone out in a kayak, canoe etc. in those conditions without a PFD is obviously not expecting it. Just the opposite in fact.

I morbidly wonder at what point, if any, does one realize they Fd up. I don’t ever want to know the answer to that. Sharks or no sharks Quint, I’m a wearing the damn PFD.

https://www.boaterexam.com/blog/2010/05/cold-water-immersion.aspx