South Fork & Henry's Fork Fishing Reports

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South Fork

South Fork, January 2nd, 2021

It looks like about 900 cfs will be the maintenance flow out of Palisades Dam until the upcoming irrigation season. That seems a bit small to some folks, but consider that tributaries add a considerable amount of water to the river on downstream at least to Heise where the flow increases to around 1300 cfs.

In any case, the South Fork is arguably our most popular river for angling. That being said, IDF&G spends a good deal of its fishing resource allocations on studying and maintaining its salmonid population. Below are results of recent studies that indicate good news for the salmonid population, the wildlife that depends on it, and anglers.

 

High trout numbers continue in the South Fork Snake River

By Pat Kennedy

The South Fork Snake River (SFSR) in eastern Idaho supports the largest river population of native Yellowstone cutthroat trout in Idaho as well as other popular game fish including Rainbow trout and Brown trout. Idaho anglers have repeatedly asked Fish and Game managers to focus management efforts on protecting native trout species when possible. This public sentiment is reflected in our state fish management plan where the goals for the South Fork Snake River include: protecting the genetic integrity and population viability of cutthroat, and reducing rainbow trout abundance to less than 10% of the trout in the upper river near Conant, as was the case in the mid-1980’s. These goals are also reflected by the Yellowstone cutthroat trout management plan. Each fall, IDFG employees use boat electrofishing techniques to estimate trout numbers in order to gauge management efforts relative to goals stated in the management plan. Results from 2020 surveys suggest two things; trout numbers are at a record high and Rainbow trout still comprise more of the population in the upper South Fork than called for in the management plan.

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Almost every year since 1986 IDFG conducted abundance estimates in October near the Conant boat ramp to monitor trout abundance in the upper river. At our Conant monitoring reach, we estimated trout densities to be 6,302 fish/mile. The 10-year average is 4,710. Good trout numbers are expected to contribute to continued good catch rates for anglers. Rainbow trout, which are the biggest threat to cutthroat trout through competition and hybridization, continue to provide management challenges. Rainbow trout made up 43.1% of the trout catch, so IDFG plans to continue efforts to lower their abundance using the angler incentive program and other tactics.

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Pat Kennedy, IDF&G

Figure 1.               Estimates of fish per mile for Yellowstone cutthroat trout (YCT), rainbow trout (including hybrids; RBT), and Brown Trout (BNT) at the Conant monitoring reach from 1982 through 2020 with 95% confidence intervals.

Figure 1

Abundance surveys have been conducted near the Lorenzo boat ramp most years since 1987 to monitor abundances in the lower river.  At Lorenzo, Yellowstone cutthroat were estimated at 1,260 fish/mile, the highest on record (Figure 2)! The ten-year average for cutthroat is 407 fish/mile. The total trout estimate was 2,650 trout/mile which was significantly higher than the ten-year average of 1,889 trout/mile. Brown trout are doing well here too with 1,390 fish/mile which is slightly lower than the ten-year average (1,477 fish/mile).

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Figure 2.              Estimates of fish per mile for Yellowstone cutthroat trout (YCT) and brown trout (BNT) at the Lorenzo monitoring reach of the South Fork Snake River from 1987 through 2020 with 95% confidence intervals.

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Pat Kennedy, IDF&G

The most important take-home message from these surveys is that trout abundance is high in the SFSR. The total trout estimate is higher than ever estimated at Conant, since 1982. Cutthroat appear to be doing fairly well, despite the continued threats from rainbow trout. Unfortunately, what’s good for one species seems to be good for the other, as rainbow trout continue to comprise a greater proportion of the population.

 

Other rivers in the western U.S. also host estimates of trout per mile in the thousands, but few boast estimates higher than 5,000 trout/mi. Within Idaho, the South Fork Boise, Big Lost, and Henry’s Fork rivers boast some of our highest abundance estimates, but none have exceeded 6,000 fish/mi. Other rivers in the west such as the Green River below Flaming Gorge reports 10,000 trout/mi, but stocked 14,500 RBT in the summer of 2020. Similarly, the Idaho rivers with high abundance typically receive at least some hatchery trout supplementation. The SFSR is not supplemented with hatchery trout. The exceptional wild trout population in the South Fork highlights the extremely high productivity observed in recent years in the river and the potential this tailwater fishery possesses. For anglers, high abundances of trout should ensure that fishing will remain great into next year and beyond.

 

 

 

 

 

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South Fork, December 1st , 2020

It looks like about 900 cfs coming out of Palisades Dam will be the basis for the South Fork maintenance flow through the winter.  Resulting flow at Hesie will be around 1300 cfs and at Lorenzo around 600 cfs.   Where roads and bank ice permit, there will be a good choice of walk-in wade fishing locations. Be aware that the South Fork River Road above Heise closes to motorized vehicle travel from Table Rock to Black Canyon on December 15th.  This closure protects wintering wildlife.

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South Fork, November 7th, 2020

Water flow in the river has been stable (about 1300 cfs at Irwin) for almost two weeks. BWOs remain active, and rubber legs and streamer patterns will produce especially under low light conditions. But winter is coming, and next week looks like ice in the guides and reels and chilled fingers expected. Is it time to clean up the gear and store it for next year? Not quite. There will be some “half decent” weather as we move through November with decreasing BWO activity and more reliance on nymph and streamer patterns for fishing success.  So enjoy the remnant of our season, and what ever you do: don’t go for a dunking!

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South Fork, October 24th, 2020

Flow out of Palisades Dam was dropped to 1680 cfs on Thursday (now 2110 cfs at Heise, 1340 cfs at Lorenzo). Great for walk-in fishing and from a boat because  low flow concentrates fish, but is not so good for them.  Let’s hope flow goes no lower with winter coming up.  The current windiness does not help any aquatic insect hatches.

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South Fork, October 20th, 2020

 

Above Menan (640x480)

Flow out of Palisades Dam has been reduced to 3160 cfs ( 3640 cfs at Heise, 1910 cfs at Lorenzo). This is great for walk-in fishing and locations for doing so are numerous.  With the wind not quite as fierce as past few days BWOs will be more active. If wet flies are preferred, drop a bead head nymph off a rubberlegs pattern. But to try these approaches, you’d best hurry. Weather this weekend looks to be awfully close to that of winter!

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South Fork October 17th, 2020

Flow out of Palisades Dam has been ramped down to 3980 cfs ( now 4610 cfs at Heise, 2380 at Lorenzo).  This makes for even more wading  locations. Even with the wind this is good BWO conditions up and down the river.  There are plenty of sheltered spots along the river, especially in side channels. Don’t forget to have streamer patterns in that fly box; they are becoming more effective each day this time of year.

Chad Larson (208-346-1459) tells us Thursday evening he lost a green & black Cabela’s backpack between Kelly’s Island and Wolf Flat.  Contents include a Pfleuger reel, multi-compartment box of flies, dual sided snap box of flies, and assorted tools.  Chad would much appreciate recovery if you find this item.

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South Fork, October 13th, 2020

From Squaw Cr. Dugway (800x600)

The river helps the BWO and mahogany dun activity by having a near constant flow ( 6050 cfs at Irwin, 6700 cfs at Heise, 3550 cfs at Lorenzo) of clear, cool water for several days, but it looks like a drop in flow out of Palisades is coming up.  Everything these unsettled days works in favor of mayfly activity except for the WIND, that is, and lately it has been fierce during afternoons when they should be most active.  So expect slower action when wind comes up.  But that is not the case with streamers. Bad weather usually means they are effective because of increased overhead cover. So continue taking BWO and mahogany dun life cycle and streamer patterns and the gear to present them during the fall season.

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South Fork, October 10th, 2020

 

Just above Heise Br. (640x480)

Flow is just a bit higher than normal for the time of year: around 6000 cfs at Irwin, 6630 cfs at Heise, 3280 cfs at Lorenzo.  Water is crystal clear and cooling.  Only sad happening is that fall colors will soon be a thing of the past. Riffle fishing seem to be picking up with BWO and mahogany dun action bringing fish up.  Add caddis activity during PM.  With a stormy weekend predicted this action may get even better, but do not overlook presenting streamer patterns.

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