Anyone who has watched the South Fork below Palisades this month has seen the river shrink. So where does it stop? The current plan says about 900 cubic feet per second. That figure is the winter target for Palisades Dam named in the October 2 Upper Snake water supply update. It is also the minimum winter discharge Idaho Fish and Game advised in 2022 to protect the recruitment of Yellowstone cutthroat in the South Fork.
This winter the target and the minimum are the same number. The river is heading there in a year when Palisades Reservoir dropped to 9% of capacity, and the whole Upper Snake system came close to its lowest carryover on record.
A dry year that a weekend storm finally interrupted
Water year 2026 did not fail for lack of precipitation. In the Post Register's October 2 water supply update, Rob Van Kirk wrote that total precipitation was slightly below average but "well in the middle of the pack." What set the year apart was that a record-low share of that precipitation was stored as snowpack. The year was also on track to finish as the second warmest in NOAA's 132-year national record.
Little snow meant little natural flow later in the year, and irrigation demand drew on storage to make up the difference. The October 8 fishing report from The Lodge at Palisades Creek put Palisades Reservoir at 9% capacity that morning. The same day, Water District 01 put the entire Upper Snake reservoir system at about 8% and projected that its end-of-year contents would land only slightly above 2003, the previous modern low.
That report also pointed to a storm forecast for the weekend of October 10 and 11:
"It could also mark the transition into the storage season, when the reservoir system begins to refill."
The storm did that. By Water District 01's October 14 report, most canals had finished the irrigation season. The weekend's precipitation had moved the system "out of drawdown and into the storage season," with storage accumulating under the 1906 Jackson and 1909 Walcott rights. The system stood at about 9% of capacity, and recharge operations in the Lower Valley were projected to begin October 20.
So the drawdown has ended, and the South Fork's ramp-down follows from that. When irrigation demand stops, operators no longer need to push storage water down the river, and Palisades outflow can fall toward its winter level.
Where the ramp-down stood in mid-October
The Post Register's October 2 update laid out the plan plainly: "Outflow from Palisades remains at around 4,000 cfs but will be reduced gradually down to its winter target of 900 cfs over the next few weeks as basin-wide diversion drops." For comparison, upstream at Jackson Lake, outflow had already been brought down to its winter target of 280 cfs.
The gauges show the reduction is underway:
| Date | Reading | Value | Source |
|---|---|---|---|
| Oct. 2 | Palisades outflow | about 4,000 cfs | Henry's Fork update via Post Register |
| Oct. 7 | South Fork near Irwin | 4,070 cfs, 48.9°F | Fly Fish Food report |
| Oct. 8 | South Fork at Irwin gage | about 4,100 cfs | The Lodge at Palisades Creek |
| Oct. 15, 7 p.m. | Irwin, provisional | 3,560 cfs | Reclamation Hydromet |
| Oct. 15, 8:30 p.m. | Irwin, provisional | 2,510 cfs | USGS |
| Oct. 15, 7 to 8 p.m. | Palisades storage | 95,881 acre-feet at 5,515 ft elevation | Reclamation Hydromet |
The two Irwin readings from the evening of October 15 differ by about 1,000 cfs. Both agencies label their figures provisional and subject to revision, and the USGS Irwin gauge page remains the place to check the live number. Either way, the river had dropped well below the roughly 4,100 cfs of a week earlier. No step-by-step reduction schedule has been published, and Water District 01 has said that operations and targets can change. Treat the 900 cfs as the stated plan, not a fixed date on a calendar.
Why 900 cfs is a biological line
The South Fork supports native Yellowstone cutthroat alongside brown and rainbow trout. Idaho Fish and Game encourages anglers to harvest rainbows on this river because they compete with the cutthroat.
A 2022 fish-management submission records that IDFG advised a 900 cfs minimum winter discharge from Palisades. The same submission warned that flows at or below that level could impair cutthroat recruitment, meaning the number of young fish that survive to join the population. In earlier Idaho State Journal reporting that followed the 2020–21 winter, an IDFG fisheries biologist described what happens as flows fall. Below about 2,000 cfs, side channels begin to dry, and juvenile trout lose places to shelter. Below about 1,000 cfs, adult fish can begin to die.
Those thresholds come from earlier years, not from a 2026 population assessment. Even so, they show what this winter's target means. At 900 cfs the river sits below the side-channel line and just under the adult-mortality line that biologist described, right at the minimum IDFG advised. This fall, the system began refilling from about 9% of capacity, and the plan on paper sits at the line.
The weeks before the river reaches its floor
None of this makes the next two weeks less worth it. A falling South Fork is one of the better stretches of the fishing year, and it opens water that summer flows keep off-limits.
Bruce Staples, writing in Fly Fish Food's October 7 South Fork report, said flows had dropped enough to offer "numerous wading locations." He described trout moving toward cut banks and vegetated edges and water coming out of Palisades clear and cold. He also noted that boat traffic was thinning and that float trips take longer to cover the same distance at low flows than they do in summer. The Lodge at Palisades Creek's October 8 report described the switch that comes with the first cloudy, cooler days. Hoppers and ants give way to Blue Winged Olives, Mahoganies and streamers, and the lodge's guides said that shift "usually brings some of the best fall fishing of the season."
The calendar from here, for a reader on October 22:
- Now through the end of October: Under the stated plan, Irwin flows keep falling toward the winter target as the last canals finish deliveries. More gravel bars and edges become wadeable each week, and floats take longer.
- October 28: Water District 01's Committee of Nine meets at 10 a.m. at the Pocatello Airport, with a virtual option. It is the body to watch for any change to how this winter's water is handled.
- October 31: The Lodge at Palisades Creek closes for the season. Its Swan Valley Fly Shop is open daily until then.
- October 31: The Fall Creek Beast trail race returns to Swan Valley for its second year, with a half-marathon at $59 and a 50K at $99. Local brothers Dillon, Quinn and Reilly Kunz organize it, and part of the course crosses their family's property. East Idaho News reported roughly 140 runners registered as of late September, against a capacity of about 300. Runners can also sign up on race day, and the organizers want people to come in costume.
The name comes from a local legend. In the same East Idaho News piece, Quinn Kunz said that a man in the 1800s claimed to have seen a giant beast in the Swan Valley area with an elephant trunk and tentacles, one that shot fire from its mouth, and that it was gone by the time he came back with others.
After Halloween the lodge is closed, the race is over, and the South Fork heads into a winter at about 900 cfs. In a year like this one, that is the minimum Idaho Fish and Game advised for the river's native cutthroat.
Water years like 2026 shape South Fork frontage and rural land in Swan Valley over the long run, not just a single season of fishing. If you own along the river, or you are thinking about what a property's water and setting will mean to the next generation, our team at Wealthwise Real Estate is glad to talk it through quietly and on your timeline. Contact Us.
