Back in high school, I lived in Iowa and was bicycling every day, no matter the weather. Christmas eve, I bundled up and went out for a ride. Tiring of the road and looking for something different, I ventured out onto the frozen lake.
As long as I rode in a straight line without braking, I was fine riding 20-25 mph across the ice. A fine, swirling snow across the surface made for a relaxing visual experience as I enjoyed the first ten minutes. The next thing I knew, I was underwater and swimming back to the surface. Adrenaline surged through my body as I hoisted myself and my soaked clothes over the edge of the ice. I must have ridden into a hole in the ice (maybe some kind of underwater spring making a warm area), rather than breaking through, or I might not have been able to get out. The ice around the edge was thick enough to support my weight. I ran 1/4 of a mile (no, I don't know what my time was) to the shore and knocked on a back door.
The next day, Christmas Day, we followed my bloody nose trail on the ice back out to the hole and fished my bicycle out.