James is right (when isn’t he???).
I only missed open water fishing for one month out of the past 12 (Feb 2006). During the rest of the winter months, I fished with relative ease by just swirling the rod tip in the drink to clear any ice build up. On a sunny day it really isn’t much of a problem at all, even with temps well below freezing.
There was one occasion that I really struggled. It was during a March IDA tournament that featured air temps at take off of 6 degrees F. Yikes, that was a COLD morning. I struggled for about 2 hours, not because of ice forming on the guides, but because the line spooled up on my reel was turning into a line-sicle. Once the sun popped out around 9:30, problem solved. That has to be my coldest open-water experience, and even then, line/ice issues were for the most part manageable.