The formal fishing season is over in SW Montana for most people but remember, many of our streams do remain open to fishing all winter long. The state of Montana believes that there is no reason to prevent anglers from enjoying a nice day on the stream when it comes along.
Generally in late fall and winter you are going to have to fish nymphs deep with weight and a strike indicator. The water will be too cold for the fish to be active enough to chase streamers and you will not find much hatch activity to provide top water dry fly fishing.
This fall the Beaverhead is much higher than we have experienced in the past several years. The river closes from Clark Canyon Dam to Pipe Organ Rock to protect spawning trout but you can fish from Pipe Organ Bridge all the way to Barrett's Diversion through the entire winter. Fish small nymph patterns like the ray charles, pink softy scud, brassies and micro may flies. We recommend sizes 18-22. Use lots of weight and fish very deep.
The Big Hole is a bit higher than normally seen at this point in the fall but that is good for anglers particularly if you want to float the river. I would suggest a larger stone fly pattern like the Pat's Stone with a small copper john dropped off the back. Use at least a BB shot and fish deep.
The Madison is very good in the off seasons. You should find fish moving from Ennis Lake up into the Varney Bridge area. As always, you should fish some type of nymph deep. The standard bead heads are always a good choice as well as the stone fly patterns. Fish about a size 8 stone fly and size 12-14 bead head. I like the lightening bugs, copper johns and prince nymphs as my dropper.
For the smaller stream fisherman we recommend the Ruby below the Ruby Dam. This stretch of the river is open year around and you should be able to enjoy some good mid-day fishing with bead head nymphs on any nice day this fall and winter.
Finally, the Jefferson is another option but as we always like to let anglers know, it is a river with a lower fish count per mile so you should not expect to have as active a day's fishing as you would on other area rivers. You can hook some very large fish on the Jeff but not a lot of fish typically.
If you are an out of area fisherman we would not suggest you plan a vacation to SW Montana specifically to fish this late fall or winter but if you find yourself in the area on business or for recreation of another type and you have a free day when the temperatures are comfortable, don't forget that you can fish most of the rivers of SW Montana all year long!