Fly Fishing Red Rock River - Below Lima Reservoir

Fly fishing Red Rock River – Below Lima Reservoir drops you into one of the quietest corners of Southwest Montana, a wide-open Beaverhead County valley of sagebrush and willow where the horizon runs a long way before anything interrupts it. The river leaves the outlet of Lima Reservoir near Monida at roughly 6,540 feet, slides past the ranching town of Lima, and works its way down to Dell at about 6,050 feet — some thirty river miles in all — before continuing on toward Clark Canyon Reservoir. Away from the water the country is arid and largely treeless, but a narrow gallery of cottonwoods traces the immediate banks below the dam and marks the channel from a long way off. This is Beaverhead River Basin water, and hardly anyone fishes it.

The Red Rock through here is a low-gradient meandering meadow river, and it behaves far more like a spring creek than a big Montana freestone. Expect quiet flats, long riffle-run sequences that tail out into soft water, gentle inside bends, and — the single most important structure in the whole reach — deeply undercut grass-and-willow banks that hang out over the current. Fish those edges first and everything else second. Below Lima Reservoir the flow regime is dictated entirely by the dam, but Lima is a shallow irrigation storage impoundment rather than a cold bottom-release structure, so what you get is an irrigation-delivery river rather than a stable, cold tailwater. Wading is moderate.

Brown trout are the story here. Montana FWP's drainage survey puts the population at roughly 600 browns and 100 rainbows per mile — a six-to-one, brown-dominated fishery, which is the opposite of what most anglers assume when they see a reservoir upstream. Rainbows are present but fewer and mostly 10 to 12 inches. The browns run noticeably larger, and a three- to four-pound fish is a genuine possibility on any given day. Mountain whitefish are abundant and will keep a nymph rig honest. Both trout species also run up out of Clark Canyon Reservoir — browns on a fall spawning migration, rainbows pushing up in spring — and those lake-run fish are the largest in the reach by a wide margin.

Midges are a constant background presence, the default answer when nothing else is showing. Blue-wing olives come off in spring and again in fall, pale morning duns and caddis carry the warm stretch of the year, and yellow sally and golden stone add bulk to the summer dry-fly menu. The slower lower water grows a trico hatch that will humble you — long leaders, fine tippet, and a good drift are not optional. The real signature of this river, though, is grasshoppers: sagebrush meadow, grassy undercut banks, and steady valley wind add up to some of the most honest hopper fishing in the region. Keep a box of streamers for the lake-run browns.

Flows are the defining variable, and the swing is dramatic. The wadeable window runs roughly 60 to 250 cfs. Year to year the pattern is bimodal — late-summer flows of 250 to 375 cfs in full irrigation-delivery years, collapsing to 15 to 25 cfs when the water gets shut off in drought years. FWP notes that dewatering can be severe, with flow ceasing entirely for days at a time in short stretches. Check the gage before you make the drive; this is not a river to gamble a long approach on. It is not floatable either — wire ranch fences cross the channel and no float operations run here.

Access is the main reason the Red Rock stays overlooked. There are no FWP Fishing Access Sites anywhere on the river, and much of the corridor is private ranchland. Public entry comes from BLM parcels below the reservoir and from county road bridge crossings — Country Bridge, the Lima town bridge, and Red Butte Bridge. Once you have entered legally, Montana's stream access law allows you to wade below the ordinary high-water mark. I-15 serves Monida, Lima, and Dell, but it does not parallel the upper river; Lima Dam sits about 11 miles east of the interstate, reached by Lima Dam Road and Red Rock Road. FWP records only about 1,000 angler-days a year on the entire reach — for a meadow river holding 600 brown trout to the mile, that is a remarkable amount of water to have to yourself, provided you time it when there is water in it.