The Northern California Fly Fishing Board

They're still there, the water has just gotten colder and has made the fishing tough. Fish generally move back into slower deeper water when it gets cold. They'll be in the same holes just a little further back. They can still be in the front of deeper holes but they'll be down on the bottom where there isn't any current. The fish "migrating" any measurable distance doesn't seem very likely to me unless you are talking about fish coming upstream from the lake to spawn. I'm guessing that the SF of the A is a freestone stream? It's been my experience that Winter fish can be lethargic and usually don't feed much during non hatch periods once the water gets really cold. It's not quite as bad in tailwaters since the water doesn't tend to get as cold as natural streams. This time of year BWO's are coming off pretty much everywhere so I would bet they are in the SF of the A too. You should see them during the warmest part of the day. Matching the hatch is a lot more important when the water gets cold since that seems to be the only time they really feed. I'd look for risers in the calm water. If I couldn't find any I'd nymph with BWO nymphs and emergers. Fishing before or after the hatch can pretty much be a waste of time.