That's my go or no-go decision maker too - line freezing in my guides. Cannot stand it, and especially bad on fly line. I paddled around the other day for a couple of hours mostly to get out of the house, but the water temps were right around 40, and that's some pretty slow fishing for Bass. If the water temps was 37 and then jumped up to 40 after a couple of warmer and sunny days, maybe. But not sitting at 40 for a week, or worse, dropping.
I love cold weather Bass fishing, paddling around in the chill with no one else in sight, or fishing from the big boat where there may be another rig parked at the ramp, but you don't see them all day, either. Suspending jerkbaits, of lightly weighted Clousers worked the same way as you would a jerkbait. I can't wait for a little warm up.