South Fork Boise River
Below Anderson Ranch Dam
SW Idaho, USA
Open live forecast →Target species: Rainbow and Brown.
Stream gauge: 13185000. Flow and water temperature update on every refresh.
Weekly AI Outlook as of 06/05/26
At 1830 cfs, the South Fork Boise is running higher than typical June levels but still very fishable. This tailwater fishery is prime for PMD emergence with water temps in the sweet spot. The cooling trend through the weekend (dropping from 78°F to mid-50s) will trigger strong midday BWO activity alongside ongoing caddis hatches. Focus on #18-20 BWO patterns during the 11am-2pm window when air temps peak, then switch to caddis emergers as evening approaches.
- Flow: 1830 cfs — elevated but manageable, wade carefully and target softer water along banks and behind structure
- Hatches: PMDs ongoing, BWOs emerging midday as temps cool, caddis in evenings — #18 olive patterns and emergers producing
- Water Temp: Tailwater holding steady around 55°F — perfect for multiple overlapping hatches through the day
- Best Window: 11am-2pm for BWO emergence, then 6-8pm caddis activity — all-day potential with pattern changes
Generated weekly from live USGS gauge readings, weather forecasts, and recent fly shop reports. Updates Friday mornings.
About this Water
- Tailwater
- Best months: Apr–Oct, peak June–Sept
The South Fork of the Boise River below Anderson Ranch Dam in southwestern Idaho is one of the West's most underrated tailwater fisheries — cold flows from the dam support wild rainbow and brown trout in a steep canyon south of Boise. The river is technical: clear water, educated fish, and the Highway 21 access can mean crowds on summer weekends. Hatches are reliable: PMD, caddis, BWO, and the famous summer Pink Albert (Epeorus) hatch.
The South Fork Boise's Pink Albert hatch — a salmon-pink mayfly emerging through summer afternoons — is one of the few significant western mayfly emergences with that distinctive coloration, producing dramatic visible rises that anglers travel specifically to fish.
January Outlook
The South Fork Boise below Anderson Ranch Dam is one of the Pacific Northwest's finest winter tailwaters. Constant dam-regulated flows and stable water temperatures keep the river fishable year-round. January midging in the canyon for dedicated anglers.
Productive Patterns
- Zebra Midge
- RS2
- WD-40
- Juju Baetis
Tips
The canyon between the dam and Pine is the prime winter section. Target the deep, slow slots with a two-midge indicator rig. The tailwater stays open and productive when every freestone river nearby is frozen.
Water Notes
Regulated 300–700 cfs. Water 44–50°F year-round. Ice-free even in hard winters. Remote but consistently productive.
February Outlook
February midging with increasing BWO activity. The South Fork Boise provides some of Idaho's finest winter tailwater fishing. The canyon setting in winter is dramatic.
Productive Patterns
- Zebra Midge
- RS2
- Vis-A-Dun #20
- Juju Baetis
Tips
The 11am–2pm window is best. Fish the slow flats below the dam. BWO activity begins on warm afternoons. Very few anglers fish the South Fork Boise in winter — an opportunity for solitude on a quality tailwater.
Water Notes
300–600 cfs. Water 44–50°F. Cold air but ice-free. Open year-round.
March Outlook
The South Fork Boise below Anderson Ranch Dam is one of the best winter tailwater fisheries in the Pacific Northwest. Midges and Baetis year-round.
Productive Patterns
- Zebra Midge
- RS2
- Juju Baetis
- WD-40
Tips
The tailwater effect keeps water temps stable year-round. Fish the slower runs with small midge rigs. BWO activity begins in earnest in March.
Water Notes
Regulated flows 300–800 cfs. Water 44–50°F year-round. Excellent clarity and consistent conditions.
April Outlook
Excellent spring fishing with BWO and midge activity intensifying. Some of the most consistent dry fly fishing in Idaho before runoff affects other rivers.
Productive Patterns
- Sparkle Dun #18
- RS2
- Elk Hair Caddis
- Soft Hackle
Tips
The canyon from the dam downstream is the most productive section. The river is narrow and technical — small presentations and careful wading are required.
Water Notes
300–700 cfs. Cold 44–52°F. Excellent clarity. Protected from runoff by Anderson Ranch Dam.
May Outlook
PMDs and Caddis join the BWO and midge activity. Peak spring fishing on a tailwater that rewards technical anglers.
Productive Patterns
- PMD Sparkle Dun
- Elk Hair Caddis
- RS2
- Pheasant Tail
Tips
The South Fork Boise rewards patience. Fish the slow flat sections with long leaders and fine tippet. The evening caddis hatch is excellent.
Water Notes
400–900 cfs. Still cold 48–56°F. Outstanding spring tailwater conditions.
June Outlook
Peak season with consistent dry fly action. Multiple hatches throughout the day make for an exceptional all-day fishing experience.
Productive Patterns
- PMD Sparkle Dun
- Elk Hair Caddis
- Pale Morning Dun
- X-Caddis
Tips
One of Idaho's finest June fisheries, often overlooked in favor of the South Fork Snake. Less crowd, equivalent quality fishing. Longer drives from population centers keep it less pressured.
Water Notes
500–1,200 cfs. Water 52–60°F. Excellent prime conditions.
July Outlook
Hopper-dropper and continued hatch activity. The canyon sections fish well through the summer due to tailwater cooling.
Productive Patterns
- Hopper-Dropper
- Elk Hair Caddis
- PMD Cripple
- Trico Spinner
Tips
The tailwater keeps the South Fork Boise much cooler than freestone rivers in July and August. This is one of the few Idaho rivers that fishes well through the entire summer.
Water Notes
400–900 cfs. Water stays 56–64°F due to tailwater effect. Fish comfortably all day.
August Outlook
Consistent fishing throughout August thanks to tailwater effect. Trico spinner falls in the morning, hopper-dropper through the day.
Productive Patterns
- Trico Spinner
- Hopper
- Elk Hair Caddis
- Beadhead Nymph
Tips
The South Fork Boise is at its best advantage over freestone rivers in August. While others struggle with warm water, this tailwater stays productive.
Water Notes
350–800 cfs. Water 56–62°F. Consistent tailwater conditions. One of August's best options in the region.
September Outlook
Fall BWO season on an excellent tailwater. Outstanding September fishing with very consistent conditions.
Productive Patterns
- Blue Winged Olive
- Elk Hair Caddis
- Mahogany Dun
- Hopper
Tips
The fall BWO hatch is reliable on the South Fork Boise. Fish the afternoon window on overcast days for the best results.
Water Notes
300–700 cfs. Water 50–58°F and cooling. Excellent fall tailwater conditions.
October Outlook
Outstanding fall fishing on the South Fork Boise. BWO and Mahogany Dun hatches drive excellent dry fly action. Brown trout are aggressive before spawning. Very little October pressure.
Productive Patterns
- Blue Winged Olive
- Mahogany Dun
- Streamer
- Copper John
Tips
The South Fork Boise in October is exceptional — large brown trout and the fall BWO hatch produce memorable fishing. The remote canyon is beautiful in October. Worth the drive from Boise.
Water Notes
300–700 cfs. Water 44–54°F and cooling. Tailwater maintains stable conditions. Prime fall fishing.
November Outlook
November is the final quality month on the South Fork Boise. Midge and BWO activity on mild days. Cold canyon conditions but the tailwater stays fishable through November.
Productive Patterns
- Zebra Midge
- RS2
- Blue Winged Olive
- Pheasant Tail
Tips
November on the South Fork Boise is underappreciated. The tailwater keeps fish active well past when freestone rivers give up. Fish the noon–2pm window for the best activity.
Water Notes
300–600 cfs. Cold 40–48°F. Tailwater still open and fishable. Off-season solitude.
December Outlook
Year-round tailwater fishing on the South Fork Boise. December midge fishing in the dam-release section. Cold but consistently productive for the most dedicated.
Productive Patterns
- Zebra Midge
- RS2
- Mercury Midge
- WD-40
Tips
The South Fork Boise is open year-round below the dam. December midging is possible on mild days in the canyon. Target noon–2pm. One of Idaho's finest winter tailwater options.
Water Notes
300–600 cfs. Water 44–50°F year-round. Open all winter thanks to dam regulation.
Hatch Calendar
| Insect | Peak | Active | Size | Productive Patterns |
|---|---|---|---|---|
| Blue Winged Olive Baetis spp. |
Apr, Oct | Mar, Apr, May, Sep, Oct, Nov | #18–22 |
|
| Midge Chironomidae |
Jan, Feb, Dec | Jan, Feb, Mar, Nov, Dec | #22–26 |
|
Access & Approach
Mountain Home, ID is the primary base. Wade access at multiple Forest Service sites along Highway 21. Idaho fishing license required.
Nearby Fly Shops
- Idaho Angler
- Dry Fly Innovations
Regulations & License
Fishing in Idaho requires a current license. Always verify season dates, bag limits, and any special-regulation waters before you fish.
Idaho fishing regulations & license →
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About Current
South Fork Boise River conditions on Current combine real-time flow data (USGS, WSC, CDEC, CEHQ), weather, tide predictions, hatch probabilities calibrated to this specific water, and recent fly shop reports from the area.
South Fork Boise River is one of 245 hand-curated waters in Current. The app and web forecast also generate AI outlooks for any unlisted river, lake, or saltwater flat anywhere in the world — drop a pin or paste a name and Current produces a fresh seasonal outlook with weather, flow context, and recommended techniques.
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