I stopped wearing a wetsuit the week before last as Folsom lake was starting to warm up pretty good. We have had a few cloudy, cold, days since then, though. Today was one of those. I really didn't feel like getting in when I got to Beals Point today and was already feeling a little chilled before getting into the water. I'm really glad I got in, though. It always feels good swimming, running, etc. once I get moving.
There were five of us in the water today. We swam straight across to the tree and stopped to wait for the last two people to make it across. I was starting to feel pretty cold standing there so followed the levy making the return trip. My form felt a little sloppy, probably because I was thinking about being chilled and not staying as focused as I could have. About half way back, I could feel the blood-flow cut off to my forearms, hands, and lower legs; They didn't really feel any more cold than the rest of my skin, being in the chilly water, but all the muscles that far out became very sluggish and weak. Not a problems for swimming, though, since that uses all the bigger muscles in closer to the middle.
This used to happen to me when I rode motorcycle year round. To keep warm on rides in the winter, my body would restrict blood flow to the arms and legs, but the core would just be radiant with heat. When I'd get to where I was going and get off the bike, the valves controlling blood flow to my extremities would all open back up and I could feel hot blood flush through my arms again as circulation returned to normal.
It's interesting having a crash course in cold tolerance while swimming, but it's a little unnerving because it takes place out in the middle of the lake. I recall, back when I used to ride lots, that staying warm was mostly a matter of keeping focused and not worrying about how cold my fingers felt. I kind of expect that if I paid lots of attention to my form and kept my body calm, I could stay comfortable for quite a bit longer in these conditions. It's also good to know that the body goes through a predictable process as it starts to cool off, so one should be able to clearly assess when it starts to become a risk to stay in the water longer. The body is highly adaptable and robust, and our limits are mostly mental in unfamiliar environments.