When it gets this cold for an extended period of time, one thing we stream & river anglers need to be concerned about is anchor ice. What is that, you ask? Well, anchor ice is ice that forms on the bottom of the stream. You might have heard that moving water never really freezes. Well, that's kinda true, but when we have prolonged nasty cold spells of arctic air, the rivers & streams can freeze not only on the surface, but also from the bottom up. That ice on the bottom is called anchor ice.
We need to be concerned about this because anchor ice can kill fish. Not only does it limit the space they have to live in, it freezes any food from the bottom they might need. You can't very well eat any bugs if they're frozen to the bottom. Plus, when it does finally thaw, all those bugs are now dead & mostly out of the food chain.
The other danger to trout & other fish from anchor ice is during a thaw. The ice doesn't just melt off the bottom, it breaks off sending large, rock-hard pieces shooting downstream below the surface at extremely fast speeds. At this time nowhere is really safe for a fish to hide, as all the cover they would use to avoid such dangers (rocks, underwater logs, etc) all have ice breaking off of them. The hit to a fish from a large piece of anchor ice can be lethal.
I wanted to show you folks who may have never seen anchor ice before just what it looks like. I found this video (below) while searching around that shows you some pretty good views of what a stream looks like when the surface ice & anchor ice are present on a stream. I think it will give you all a good idea of what I'm talking about here.
I hope your new year is off to a great start & that you're all staying warm!!