Big Lost River
BIG LOST RIVER
ReportOCT 28 — NOV 4, 2026
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Flow
56CFS
BIG LOST RIVER BL MACKAY RES NR MACKAY ID
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Water Temp
—
Updated 2026-10-27
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Weather
22–46°F
Partly Cloudy
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Reported By
Bruce Staples
On the water
The Big Lost River below Mackay Dam is running at 56.4 cfs (gauge height 1.46 ft) — very wadeable but demanding, with skittish fish pushed into the deepest slots. Cold overnight lows in the low-to-mid 20s and sunny daytime highs in the low-to-mid 40s set the stage for a focused mid-day BWO and midge window.
From the ShopBruce Staples · October 28, 2026
Flow below Mackay Dam is about 75 cfs, making wading very safe. The low flow makes fish skittish and concentrated in the deepest water. Best times to fish are mid-days, with some BWO and midge life cycle patterns. Overcast days have the best numbers of BWOs emerging.
Frosts have diminished the number of bankside terrestrial insects. Small nymph patterns can provide day-long action. Try October caddis patterns as evening approaches.
What's Working — Hot Flies
Hatch Chart
| Insect | Size | Activity | Prime Time |
|---|---|---|---|
| Blue-Winged Olive (BWO) | #20–22 | Moderate — best on overcast days | Mid-day (11am–3pm) |
| Midge | #20–24 | Steady — life cycle patterns (larva, pupa, adult) | Mid-day, with some morning activity |
| October Caddis | #10–12 | Light — fish as evening approaches | Late afternoon into evening |
| Aquatic Nymphs (general) | #18–22 | Consistent all-day subsurface action | All day |
Best Time Window
- MID-DAY (11am–3pm): Prime window for BWO and midge life cycle patterns — overcast days will produce the best dry-fly and emerger action.
- ALL DAY: Small nymph patterns (Pheasant Tail, WD-40, Juju Baetis) fished deep in the main channel slots will produce consistent action regardless of conditions.
- LATE AFTERNOON INTO EVENING: Switch to October caddis patterns as light fades — the staffer specifically calls this out as the evening approach.
Guide's Tip
From the benchWith flows this low and fish pushed tight into the deepest seams, presentation is everything — long leaders, fine tippet, and upstream or reach casts are essential to avoid spooking fish. If you want to cover the full BWO life cycle the staffer recommends, consider rigging a small nymph like a Juju Baetis or WD-40 under a midge pupa dropper, then switching to a dry or emerger when you spot rising fish mid-day. Note: if you have a specific October caddis dry or soft-hackle wet in your box, those are worth trying at dusk as the staffer suggests — no exact catalog match exists, so check the shop's loose fly bins.
Main Species
Rainbow Trout
Brook Trout
Mountain Whitefish
