Flow out of Palisades Dam was raised to 3430 cfs On Thursday, April 15th ( now 3880 cfs at Heise, 2100 cfs at Lorenzo) continuing the stair-step increase defined in the April 13th report. These flows are a bit below the mean flows for this date. Use the same flies and the same strategies we suggested in the April 13th report. Water remains clear and cold.
Flow out of Palisades Dam was increased from around 1750 cfs to 2460 cfs (2970 cfs at Heise, 1700 cfs at Lorenzo) last Friday. River water is cold and clear, in fishing condition throughout, but too cold for anything but midges to hatch. Look for USBUREC to raise flows in a step-wise manner from now on to the irrigation season. Rubberlegs, big stonefly nymph patterns and streamers work well as do small nymph patterns around riffles. All boat ramps are open. The USBLM Stinking Springs Human Entry road closure will be lifted at sunrise on May 1.
Water is back in the Dry Bed because irrigation structure repair there is complete.
Expect to have plenty of company if you visit the river from the Ora Bridge launch down to the Chester launch. BWO and midge life cycle and stonefly nymph patterns along with streamers under low light conditions are best bets for action. With more river to visit from Stone Bridge to Ashton, visiting anglers are more dispersed than in the river below Ashton Dam.
Here is Rob VanKirk’s latest summary of snow pack and water conditions in the Henry’s Fork drainage. Notice that snow pack conditions appear to be a bit below normal at the time of his report.
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Yesterday was dry yet again, but at least temperatures were cooler. Mean temperature was 9 degrees F below average and the coolest since March 31. Water-year precipitation to date stayed at 81% of average. Despite cool temperatures, all but one SnoTel station lost snow water equivalent (SWE) yesterday. Island Park lost the most, at 0.5 inch of melt, and the watershed total was 0.2 inch. Melt rate has averaged 0.13 inch/day over the first 12 days of April so far. SWE is 78% of average and lower than it was on this date in 2016, the last very dry year experienced in the watershed.
Light precipitation—in the form of snow at all elevations—is expected tomorrow and Thursday. Forecast amounts range from around 0.1 inch in the northeastern corner of the watershed to 0.5 inch in the southern part of the Teton Range. Valley areas and the Teton subwatershed are expected to receive the highest amounts. Cool temperatures will stick around through the end of the week. Warm, dry conditions are expected after that.
Natural streamflow continued to drop yesterday, despite ongoing snowmelt. Natural flow was 84% of average yesterday: 81% in upper Henry’s Fork, 83% in Fall River, and 91% in Teton River. Diversion continues to increase slowly, although data are not yet being reported for all canals. Moisture availability in the agricultural areas—defined by my crude difference between precipitation and evapotranspiration—continues to drop and is now almost 7 inches below average. I have already had to extend the vertical axis on the chart twice since last summer and may need to do so again in a week or so.
At an average outflow of 418 cfs, Island Park Reservoir gained 22 ac-ft yesterday. Current content is 120,795 ac-ft (89% full), compared with an average of 115,907 ac-ft (86% full). Although ice is starting to melt at the edges at some locations around the reservoir, Fall River Electric personnel report solid ice cover around the dam.
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Watershed SWE
Natural Stream Flow
Another few days of sunshine and wind will clear all the snow from Stone Bridge boat ramp. Flow is normal and water is clear. Floating the river from there on down to Ashton offers good fishing for those presenting stone fly nymphs and such fished deep. Some BWOs emerge during PMs to offer some dry fly fishing.
Below Ashton Dam windy days make fishing tough and blows away any midges and BWOs making the mistake of emerging. During calm days top water fishing for these can be good. Use life cycle patterns for each. Streamers produce when presented deep and around overhead cover near banks out of the sunlight.
Flow out of Palisades Dam was essentially doubled to 1790 cfs on March 29th. This begins flow increases to answer irrigation demands for the upcoming growing season. We will keep track of these increases throughout the season and log them on this fishing report.
Flow out of American Falls Dam was raised from 1250 cfs to 2430 cfs yesterday. A visit to fish is a good option, but be careful when wading.
The Henry’s Fork below St. Anthony is a productive fishery with an increasing brown trout population. Recently IDF&G fisheries personnel have completed a survey of its salmonid population. The results of this survey are given below.
Trout Populations are Strong in the Henry’s Fork near St. Anthony
By John Heckel
Regional Fisheries Biologist
In early October 2020, we conducted our 6th population estimate on the St. Anthony reach of the Henry’s Fork of the Snake River. This estimate is conducted in the fall every three years and extends from the Railroad Bridge downstream to the Red Road Bridge. Based on our sampling data since 2010, we can see an increasing trend in Brown Trout abundance in this reach.
We can see in the figure above that the number of Brown Trout per mile has been increasing since we started surveying the reach in 2004 while Rainbow Trout abundance has remained low and relatively constant. Currently, Brown Trout make up 96% of the trout composition in this reach where we caught 1,468 trout in total. As can be seen in the images, there are some very large Brown Trout with fish up to 25” in this reach!
The trout population in this portion of the Henry’s Fork is managed as a wild trout fishery, so these large trout captured in this reach are in fact wild fish. Therefore, referring to the length distribution of fish captured here, this section of river grows some very large trout.
Although water temperature in this section of the Henry’s Fork can become warmer than 70°F during portions of the summer, trout can find thermal refugia from groundwater and spring inputs that help coldwater fish remain cool. In addition to Brown and Rainbow trout, we also estimated Mountain Whitefish abundance in the reach. There were 685 whitefish per mile. Based on our length frequency data from Mountain Whitefish we observed several age classes present, which is evident by the multiple peaks in different length groups.
Survey results indicate sport fish populations in the St. Anthony reach are healthy and in good numbers. Managing this section of the river as a wild trout fishery with a 2 trout limit appears to be conducive for growing large fish and allowing population numbers to increase.
2021 fishing and boating regulations for the Park are in this link (note the fee increases and justification for such). Final-signed 2021 Fishing Vendor Permit Letter
The flow out of American Falls Dam was raised from 370 cfs to 1250 cfs on 3/18. That means you’d better hurry if you want to fish the river below with relatively easy access! Wading is still safe, but more flow increases are coming making wading tougher and spreading fish throughout the river. Streamers pitched and retrieved or drifted under an indicator at taking depth remain as effective strategies.
Flow out of American Falls Dam remains just under 400 cfs, but any day a BIG increase will happen to satisfy Magic Valley agricultural demands. Streamer presentation remains the name of the game. The further downstream from the dam one goes, the fewer anglers will be encountered.