Below Mackay Reservoir
As of September 11, 2026, the Big Lost River is fishing Fair (7.3/10): flows are 284 cfs, Tricos activity, reported by 1 shop.
Last updated
Reports indicate good conditions. flow at 288 cfs.
Conditions are holding steady since the previous update.
Cold tailwater below Mackay Reservoir. Large rainbows. Best late June through September.
A quick view of the latest report, gauge, hatch, and fly data available for this water. Missing observations are left unreported rather than estimated.
Current reports mention Tricos, Baetis, Crane Flies. Recommended flies include Crane Flies, Blue Wing Olive, Zebra Midge, Streamers.
Recent reports mention Below Mackay Reservoir, Below Mackay Reservoir; North Fork and East Fork also mentioned, below Mackay Reservoir; also North Fork, East Fork, and main stem upper sections.
Access and seasonal rules can change. Check current regulations and closures with Idaho Fish and Game ↗
Big Lost River location
43.9392, -113.6483
Current Flow
284cfs
| Insect | Stage | Timing |
|---|---|---|
| Tricos | adult | midday |
| Baetis | adult | midday |
| Crane Flies | adult | — |
| Crane Fly | adult | midday |
| Cranefly | adult | — |
| Trico | adult | morning |
| PMD | — | morning |
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Current options in Idaho.
Great · Updated 1d ago
Great · Updated 1d ago
Fair · Updated 1d ago
Fair · Updated 1d ago
Silver Creek Outfitters
Flows are wadeable but pushy at around 300 cfs. Tricos and Baetis are hatching as the day warms, with giant crane flies effective on the surface; nymphing with small Baetis or midge patterns keeps fish coming in the slower afternoon.
Silver Creek Outfitters
Flows at 300 CFS and dropping; Tricos and Baetis hatch as the day warms with giant crane flies skittered on the surface. Bug activity slows in the afternoon but nymphing remains productive with small Baetis or midge patterns.
Silver Creek Outfitters
Flows around 340 CFS make the river accessible for strong waders, with feeding trout found in riffles, buckets, and along shallow edges. Tricos and Baetis are active in the mid-morning; afternoon fishing slows but nymphing still produces.
Silver Creek Outfitters
Flows are around 350 CFS (reported at 321 CFS) and falling. Morning Trico hatch is decent with some Baetis, but afternoon fishing can slow considerably once hatches are done; nymphing will still produce fish. Reservoir turnover may cause flows to go off-color temporarily.
Silver Creek Outfitters
Flows around 400-416 CFS are limiting access on the Big Lost below Mackay. Trout are well-seasoned and selective, requiring fine tippets and precise presentations; mornings offer Tricos, Baetis, and craneflies.
Silver Creek Outfitters
Flows are slightly high at around 400 cfs but fishable for confident waders. Tricos and PMDs hatch through the morning and taper off in the afternoon, with a few Crane Flies also drawing strikes.
Silver Creek Outfitters
Flows below Mackay are near 400 CFS, slightly high but fishable for confident waders. Trico and PMD hatches occur through the morning and fade in the afternoon; crane flies can draw fast takes.
Silver Creek Outfitters
Flows below Mackay are near 400-457 cfs, still a bit high but fishable for confident waders. Tricos and PMDs hatch throughout the morning and taper off in the afternoon, with crane flies also present.
Silver Creek Outfitters
Flows remain high at around 450-457 CFS limiting access, but decent Baetis, PMD, and Trico hatches occur throughout the morning and dwindle in the afternoon. Craneflies are also active and can draw vicious strikes.
Silver Creek Outfitters
At 433 cfs the river is still very high and difficult to cross, but strong waders can move about. Good morning hatches of PMDs, Baetis, Craneflies, and Tricos are present; nymphing remains the most productive technique.
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