Big Lost River
BIG LOST RIVER
ReportNOV 4 — 11, 2026
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Flow
73CFS
BIG LOST RIVER BL MACKAY RES NR MACKAY ID
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Water Temp
—
Updated 2026-11-04
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Weather
29–50°F
Mostly Sunny
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Reported By
Bruce Staples
On the water
The Big Lost River below Mackay Dam is running at 72.6 cfs (gauge height 1.54 ft per USGS), making for safe wading but gin-clear, low water that demands a stealthy approach. Today's mostly sunny skies will temper BWO activity, but Thursday's forecast cloud cover sets up the best dry-fly window of the week.
From the ShopBruce Staples · November 4, 2026
Big Lost River, November 4th, 2026. Flow below Mackay Dam is about 75 cfs, making wading very safe, but some stealth is required. The low flow makes fish skittish and concentrated in the deepest water.
Best times to fish are mid-days with BWO and midge life cycle patterns. Overcast days have the best numbers of BWOs emerging. 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 | Midday (11am–2pm) |
| Midge (life cycle) | #20–24 | Light to moderate — consistent | All day, peaking midday |
| October Caddis | #10–12 | Light — evening activity | Late afternoon into evening |
Best Time Window
- MIDDAY (11AM–2PM): Prime window for BWO hatches and midge activity; overcast days will produce the best dry-fly action
- ALL DAY: Dead-drift small nymphs (midge and BWO patterns) through the deepest runs for consistent hookups
- LATE AFTERNOON–EVENING: Switch to October caddis patterns as light fades and evening activity picks up
Guide's Tip
From the benchLow, clear water on the Big Lost calls for long, light tippet and a slow, deliberate approach — spook one fish and you may put down the whole pool. Fish are stacked in the deepest available water, so get your small nymphs down quickly with a tight-line or indicator rig. Thursday's cloudy forecast looks like the best BWO dry-fly opportunity of the week, so plan your midday session accordingly. If you have October caddis soft-hackles or wet flies in your box, swing them through the tailouts as the light fades.
Main Species
Rainbow Trout
Brook Trout
Mountain Whitefish
