I fished a small river one winter when there was shelf ice along the sides and the rocks on the river bed had ice as well.....very odd I thought with the river running in between. The water was so low and clear that the fish would just bury themselves into any cover they could find. I remember looking upstream under a large chunk of concrete (reminant of old bridge washout) and with only the down stream edge of the concrete above the stream bed, I could see three steelhead tails waving at me....no way to present anything as the upstream edge of concrete was well buried in the bed.