Fly Fishing Musselshell River - Martinsdale

Overview

The Musselshell River winds through central Montana's agricultural valley from the confluence of its North and South Forks near Martinsdale to the Highway 191 bridge at Harlowton. Open grasslands, hay meadows and distant mountain ranges frame a narrow river of twisty meanders, undercut bank pools, riffles and slow-moving runs. Overhanging willows and grass banks provide cover, making a careful approach and a controlled drift part of the fishing.

Irrigation diversions and dry weather can reduce summer water levels, while warmer conditions change the appeal of the trout fishing. Look for spring and fall olive activity, caddis through spring and summer, and terrestrials beside the grassy banks when water conditions suit. Streamers offer another way to work undercut cover, particularly on overcast days.

Water and Character

The Musselshell has a spring-creek feel despite being a freestone river. Its narrow channel bends through gravel, cobble and silt, with willows and grass overhanging the banks. The gentle valley gradient creates a mix of undercut bank pools, shallow riffles and slower runs. Read each bend separately: the deeper outside bank and the seam below a riffle call for different casting angles and drifts.

Brown trout are part of this upper river's fishery. Keep your shadow off the water and fish the near lie before casting across it. A low approach helps beside brushy banks, where both movement and a careless backcast can spoil the presentation. Give the dark slot beneath an undercut a controlled drift rather than covering it with repeated long casts.

Seasonal Flies and Presentations

Blue-winged Olive patterns belong in the spring and fall box, especially for surface activity on overcast days. Carry caddis for spring and summer, with Pale Morning Duns as another option when visible insects and rises call for them. Small nymphs and midges let you work below the surface when the pools are quiet.

Grasshoppers, ants and beetles are useful summer options along the grassy banks. Place the fly close to cover, then watch how the current carries it past the undercut. A terrestrial does not need to land in every part of a pool; concentrate on the feeding lane you can reach with a clean drift.

For spring and fall, try a streamer beside deeper bank cover or through a pool. Overcast conditions are a useful time to give that approach a turn. Change the casting angle and retrieve to keep the fly near the cover rather than relying on a large fly or fast strip alone.

Changing Water

Summer irrigation and dry years can reduce the water available in this valley stream. As levels recede, a riffle may carry less water and the deeper bank pools become more distinct. Warm conditions can narrow the trout-fishing opportunities, particularly farther downstream. Let the day's water and visible activity guide where you spend your time rather than treating the whole Martinsdale-to-Harlowton stretch as uniform.