Fly Fishing Poindexter Slough - Dillon

Overview

Three miles south of Dillon, the lower Poindexter Slough winds through a broad hayfield valley before joining the Beaverhead River. This meadow channel follows the Beaverhead's old bed and carries a mixture of groundwater and river water admitted through a headgate farther upstream. Snaking S-curves, willow-lined runs, undercut grassy banks and gravel riffles feeding deeper pools give the mapped fishing-access-site reach its spring-creek character.

Fish it with a low profile and a deliberate drift. Watch for feeders against the undercuts and beneath overhanging grass, then work the seams below the riffles with small nymphs or a dry-dropper. A long leader helps with presentations on the flats, while a small streamer fished slowly through a pool offers a different approach. Diversion water and rain can change the level and clarity, so read the channel before choosing a lie.

Groundwater, Headgates and Reading the Water

For much of a century, flood irrigation on the surrounding hayfields seeped into the water table and returned to the slough, giving this former Beaverhead channel a spring-creek character. The shift toward pivot irrigation changed those inputs, and diverted Beaverhead water became more important. Groundwater and headgate operations both influence the water you see today.

The channel sits at about 5,150 feet in a broad valley bottom, with open grassy banks that offer little cover for an approaching angler. Stay back from the edge and watch a flat before casting. Clear water calls for particular care with your shadow, leader and drift.

Irrigation season changes the equation. More water admitted through the headgate can alter the pace of the riffles and the shape of the pool seams. Silty diversion water or a valley rainstorm can leave the slough murky. There is no live gauge on Poindexter Slough; judge level and clarity at the channel rather than treating the neighboring Beaverhead's reading as a substitute.

The Restoration Comeback

Silt accumulation changed the slough's pools and gravel habitat as irrigation practices changed. From 2015 to 2018, the Beaverhead Watershed Committee, Montana FWP, the canal company, landowners and local businesses worked on the channel. The project installed a larger upstream headgate, replaced the canal diversion, removed sediment, narrowed and reshaped the channel, rebuilt riffles and pools, and planted willows.

Those riffle-to-pool transitions are useful places to start reading the water. Follow the current from the faster gravel run into the softer seam, then look along the pool edge for an undercut or overhanging grass. Adjust a nymph's depth to the lane rather than covering every part of the pool with the same rig.

Hatches Through the Seasons

Winter fishing is a slow, low game. Carry midges for surface activity on mild afternoons, with scuds, sowbugs, worms, leech patterns and small dark streamers as subsurface options for deeper pools. Watch for rises before committing to a dry fly.

Cloudy spring afternoons are a reason to carry Blue-winged Olive patterns, and caddis belong in the warmer-weather box. Between surface activity, try small olive or black nymphs, including bullet or perdigon styles, or a small streamer along a defined seam.

Summer suggests a morning-and-evening approach: Pale Morning Duns early, caddis and yellow sally patterns later, and trico imitations for a late-summer spinner fall when visible insects and rises call for them. Match what you observe on the flat instead of expecting a fixed hatch schedule.

As the grass browns, hoppers, ants and beetles offer another presentation along the undercut banks. In cooler fall weather, work a small streamer slowly and low through a pool or beside the bank cover. Let the fly follow the softer lane rather than stripping it quickly across several currents.

Tactics for Small Water

Rig for spring-creek work. A 4- or 5-weight rod with a 12-foot leader tapered to 5X or 6X suits delicate dry-fly presentations, with tippet adjusted to the fly and cover. Approach along the open grassy banks with a low profile, stay back from the edge, and watch before you cast.

Cast to fish feeding tight against the undercuts and into the shade lines beneath overhanging grass, sight-fish risers on the flats, and run a dry-dropper or a pair of small nymphs through the seams below each rebuilt riffle. Work the deeper pools with a small streamer on a slow, low retrieve. Poindexter Slough rewards patience and precision more than distance.

Nearby Waters

Poindexter is the small-water counterpoint to the neighboring Beaverhead River – Twin Bridges. The Big Hole River – Wise River and Ruby River – Alder offer other river settings in the region.