When the air temps and the water temps added together are less than 100 degrees, there is severe risk of hypothermia associated with any kind of dunking.
This is the annual reminder to dress for the water temps rather than air temps (in general, of course), use dry clothing (I use a dry top and waist high waders, a drysuit would be better), have your bailout bag with you and be sure it has fire starting materials in it that you know how to use when your hands are shaking, keep high-energy food in it, and a spare set of clothing, plus maybe some form of instant shelter (I keep one of those astronaut blankets). If your water has rated rapids, add a full number to them for when you consider what you can handle (i.e., if you’re usually a class 3 paddler, consider what would normally be a class 2 to be a class 3), don’t go alone, etc.
There’s a million other things to consider, but the point is … be prepared to get dry and warm fast if you get wet, and assume that you will get wet.
Thanks for the reminder. What brand dry top? I need XXXL. I've been going with neoprene chest waders and breathable rain jacket. No cotton. I always have a dry bag with a change of close and plan to get out and dry asap should I go in. I don't fish open water and I portage Class II when possible. I don't go out alone and always where my pfd.
So far the water temps down here have been in the mid 50's with ambient temps from upper 50s to mid 60's. I'm not sure yet how low I'm willing to go with respect to temperatures and the clothing I have.
Immersion Research That’s what I wear. I find that paddle wear seems to run small. While I usually wear an XL, I bought a XXL drytop. I’m not sure who carries larger sizes, but I expect you’d be able to get one on-line.