Last January we had a real nice 42 degree day and I decided to spend the day at the river. It was sunny and I was dressed for the cold(ish) air. I found a comfy spot to pan about two gallons of material and afterwards when I attempted to stand up I found that my heels had gone completely numb because my water boots are not insulated. This shouldn't have been a surprise to me as I am a snowboarder and know quite well the value of proper clothing for the weather. I guess this just shows that even though the air may be warm(ish) the water can still be deadly cold.
I'll have to get better boots, the rivers here are usually real low in the winter.