The largest population of trout are located from the park's boundary downstream into the Gallatin valley. The Big Sky area offers many public places to access the river. With highway 191 following the river there is almost a pull out on every turn. With its spectacular scenery in the canyon and fast pocket water, riffles and runs it is hard to find a more compelling area to fish so close to Bozeman. In the canyon section the average size trout is 8-12 inches. There are some larger trout in this area but with the cold mountain water the growing season is considerably shorter. Once you leave the canyon section the river passes through the Gallatin valley. Access is limited to state owned fishing sites and passes though many ranches and private land. The fish size increases in this area as the water temperatures increase downstream. The Gallatin river sees many different hatches throughout the year and the trout are eager to take advantage of the abundance of insect life throughout the river. While not supporting the largest trout in our area the Gallatin River does sustain a healthy population of wild trout that accommodate every skill level.
Spring weather brings on the first major hatch of the season on the Gallatin River. Blue winged olives or baetis emerge and the trout gorge themselves on the first major hatch of the season. The trout of the Gallatin river are not picky on a whole and basics patterns such as parachute adams or royal wullfs will generally fool the majority of trout. When the baetis are not hatching nymphing with pheasant tails and similar mayfly nymphs are productive.
As the water heats up so does the insect activity. The Gallatin River has a prolific Salmonfly hatch that starts just downstream from the canyon section and works its way up river to Yellowstone National Park. These extra large dry flies hit the water hard and the fishing can be frenzy like. Following the salmonflies are their close cousins the Golden Stonefly and many mayflies such as Pale Morning Duns (PMD's). The caddis start to heat up and the evenings sky can be filled with the adults fluttering above the banks. Other hatches of importance on the Gallatin River during the summer are Yellow Sallies and Spruce Moth's. This season on the Gallatin River is peak dry fly fishing. The fish will typically move into the faster riffles of the Gallatin during the summer. Because of the fast moving currents and eager trout fishing many different attractor patterns is very successful. A royal trude or elk hair caddis in a size 14 will cover many different insects from caddis, yellow sallies to spruce moths. The terrestrial fishing can be very good in the park and in the valley sections. As the Gallatin River passes through either the meadows or agriculture sections there are an abundance of grasshoppers, beetles and ants available to the trout.
Fishing on the Gallatin River during the fall months continues to be productive until the water temperatures drop too low. A smaller baetis or blue winged olive emerge in the size 18-20's. The trout of the Gallatin River start moving back into the deeper runs and nymphing is the most productive way to catch these trout as winter approaches. Streamer fishing can be very effective as the brown trout get aggressive as the spawn approaches. Smaller streamers fished on a floating line pulled across likely spots can get rod jerking strikes.
With its close proximity to Bozeman the Gallatin River is a great choice to fish when fishing during the winter. The trout move into the slower, deeper runs to conserve energy. Fishing with various stonefly nymphs and midge patterns is consistent. On warmer days there is always a possibility to find trout rising to small midge patterns. The Gallatin River is a great place to fish on a ski vacation or if you just need to fill a few hours on a winter day.
In conclusion the Gallatin River is great river for all skill levels to have success. With its ready and willing trout and spectacular scenery the Gallatin river has just about everything someone would want out of a blue ribbon stream. It is no wonder that Robert Redford picked it for many of the scenes in the movie A River Run's Though It.