Flow out of American Falls Reservoir is in an increasing mode as downstream irrigation demands for water are beginning. Yesterday flow was increased from around 440 cfs to 1180 cfs. Wading downstream of the dam can be dangerous during increasing flows. If you are fishing within earshot of sirens and whistles coming from the dam, get out of the water ASAP!
Flow out of Mackay Dam is about 75 cfs. Water management priority is to fill Mackay Reservoir, so look for low flows until irrigation season begins. The low flow makes for easy wading and concentrates fish into deeper water. Broken snow and ice prevails along banks and is receding. Midge and BWO life cycle, small bead head nymph, medium sized woolly bugger, and peacock leech patterns bring action.
With Palisades Reservoir filled about one third of capacity and out-flow about half of in-flow, it is going to take a lot of run-off to come close to filling before irrigation season begins. Outlook for enough snow accumulation needed to do so becomes more unlikely with passing days. So it looks like current flow in the river below Palisades Dam ( 874 cfs at Irwin, 1300 cfs at Heise, 700 at Lorenzo) will hold well into run-off season.
Under current water conditions (cold and clear), the best fly fishing strategy is to present streamer, nymph, and rubber leg patterns into deeper holes and runs using full sink or sink tip lines and stout leaders. Consider that winter is the toughest time for fish to survive. Therefore using stout leaders allow them to be played more quickly giving a better chance for survival after being caught and released. The river needs to warm for any good top water fishing to take place.
At the first off April, flow will be shut off in the Dry Bed for irrigation structure maintenance. During this time IDF&G allows a salvage situation there where fish may be harvested by any legal means rather than being wasted. Consult current on-line or hard copy fishing regulations for salvage specifics.
Excerpts from Dr. Rob Van Kirk’s Henry’s Fork drainage water report of this morning are below.
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Mean temperature yesterday was 2 degrees F below average, extending a streak of nine consecutive days of temperatures at or below average. With snowpack as low as it is, cold weather is critical to keeping that snow on the ground as far into the spring as possible. After a dry day, snow water equivalent (SWE) dropped back to 69% of average yesterday, while water-year precipitation stayed at 83% of average.
Current SWE is still ahead of that for the date in 2001 and 2010. Subsequent spring and summer weather differed substantially between those two years, resulting in two very different outcomes for the water year as a whole. April-September precipitation in 2001 was 21% below average, while that in 2010 was 19% above average. That difference resulted in 2001 ending up with the lowest natural streamflow in the 1978-2021 record, at 73% of average, compared with 75% of average in 2016 and 76% of average last year. By contrast, natural flow in 2010 ended up at 87% of average, ranking above the 33rd percentile of water years since 1978. So, a wide range of outcomes is still possible, although anything close to average water supply is not one of them.
Light precipitation is expected this afternoon through tomorrow and again on Saturday night and Sunday. Total precipitation amounts over the next week are expected to range from around 0.1 inch along the western edge of the watershed to around 1 inch along the Wyoming border. If those totals are realized, precipitation this week will be about the same as it was last week and close to average for mid-March. Temperatures are expected to stay near average. After that, above-average temperatures are in the forecast beginning next Tuesday, although long-range outlooks do not show any strong indication that either temperature or precipitation will deviate much from average.
Stream gages are starting to come back on line after a very long period during which ice has prevented real-time flow observations. The St. Anthony gage on the Henry’s Fork and Ashton gage on Fall River are the first two to return to real-time transmission. Based on data available as of yesterday, natural streamflow is in the range of 75-80% of average in both the upper Henry’s Fork and Fall River.
Island Park Reservoir gained 232 ac-ft yesterday and is 87% full, compared with 80% full on average. Reservoir content will reach 120,000-123,000 ac-ft by April 1.
Rob Van Kirk, Ph.D.
Senior Scientist
P.O. Box 550
Ashton, ID 83420
208-652-3567 OFFICE
208-881-3407 CELL
208-652-3568 FAX
There is access at several places along the river above American Falls Reservoir. Some include below Gem Lake Dam, around the Shelley I-15 connector, near the Firth boat launch, the Riverside access just below Blackfoot, around Tilden Bridge, and near McTucker Ponds. In all these locations river flow is lower than normal and water is clear. Presenting streamer patterns gives the best chance of success. Below American Falls Dam it’s a bit different. Some access is through muddy roads. The reservoir is about two-thirds full and low flows in the river below (currently about 450 cfs, but somewhat discolored) will continue until it is at capacity.
Nicer but unsettled weather is predicted for the coming week. With increasing BWO activity on the lower river, some decent top water fishing should take place but river still has limited approaches. Streamer and stonefly nymph patterns remain effective when presented in deeper runs and holes where you can get to them..
Excerpts from Dr. Rob Van Kirk’s Henry’s Fork drainage Snow Water Equivalent (SWE) report of yesterday, March 11th, are below. The data give a grim picture of current SWE in the area.
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Yesterday morning was the coldest in the watershed since December 17, 2016. In the 12-station 1989-2021 record I use for the whole watershed, yesterday’s minimum, mean, and maximum temperatures all set new records for the date. The low of -16.5 degrees F broke the old record of -3.2 degrees set in 2006. The daily maximum of 17.0 degrees broke the old record of 21.1 degrees, set in 2009. The daily mean was a whopping 27 degrees below average for the date and the second coldest day of the winter, behind January 1. That beat the old March-10 record by 9 degrees. Even at stations with very long periods of record, yesterday’s low temperature broke records for the date by wide margins. Idaho Falls set a new record low of -7 degrees, breaking the old record of 4 degrees, set in 1969.
No precipitation was recorded yesterday, dropping the water-year total to 82% of average. Snow water equivalent (SWE) stayed at 68% of average. After another day of below-average temperatures, forecasts and long-range outlooks all call for temperature and precipitation near climatological averages. In the short term, light precipitation is expected on Sunday, with slightly heavier precipitation on Tuesday and Wednesday. The latest 7-day precipitation forecast looks a little better than it did yesterday, with 0.25-0.5 inch expected over most of the lower elevations of the watershed and up to 1.25 inches along the Teton crest. If realized (big if), that would be roughly average for this time of year.
As you might imagine, stream gages throughout the watershed remain affected by ice. The Island Park and Ashton gages are the only two that have provided reliable data all winter, and both show natural flow in the upper Henry’s Fork at around 75% of average.
Reservoir fill rates were even lower yesterday than they were on Wednesday. Island Park Reservoir is 86% full, compared with 79% on average, and the three reservoirs in the watershed are 87% full, compared with 84% full on average. The upper Snake River reservoir system is 50% full, compared with 74% full on average.
Rob Van Kirk, Ph.D.
Senior Scientist
P.O. Box 550
Ashton, ID 83420
208-652-3567 OFFICE
208-881-3407 CELL
208-652-3568 FAX
Springfield Reservoir is producing some fishing success even though water remains cold ( mid 40’s in degrees Fahrenheit). Leech and small nymphs patterns and fly rod jigs presented on intermediate lines work. Try suspending small nymph and midge pupa patterns under an indicator on a floating line to find the taking depth.
Access to the lower river from the Ora bridge downstream to Chester is opening up. Increasing BWO activity during afternoons and midge hatches are providing some top water fishing that will increase as we move through this month. Life cycle patterns of these insects will produce. Streamer and giant stone fly nymphs will attract post-spawning rainbows almost anywhere in the river.
Fun Farm Bridge at Dusk
Excerpts from Dr. Rob Van Kirk’s Henry’s Fork drainage water status report of this morning follow.
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Mean temperature yesterday was 12 degrees F below average and will stay that cold for the next several days. Snowfall arrived yesterday evening as forecast, but only a few hundredths of an inch were recorded through midnight, mostly in the valleys. Widespread snow is expected today, accompanied by strong winds and very cold temperatures this afternoon and evening. Unfortunately, water-equivalent totals now look to be lower than anticipated yesterday, a consistent pattern over the past two months. The heaviest snowfall appears to be headed to our south again, as happened a few days ago. More precipitation is expected Sunday and into next week, but this far out, forecast precipitation could easily disappear.
At an average outflow of 214 cfs, Island Park Reservoir gained 201 ac-ft yesterday and is 85% full, compared with 79% full on average. Yesterday I reported that the mean winter (December-February) outflow from Island Park Reservoir was 218 cfs, compared with 360 cfs on average. Winter flow in the Buffalo River was 200 cfs, compared with an average of 214 cfs, so total flow through Box Canyon—the most important variable determining survival of juvenile trout—was 418 cfs, 73% of average. However, natural stream flow was much lower than average this winter regardless of the effect of storage in Island Park and Henry’s Lake. In absence of the two reservoirs, stream flow through Box Canyon this winter would have been only 516 cfs. Thus, the actual stream flow through Box Canyon this winter was 81% of the river’s natural flow, not a bad outcome following last year’s very dry irrigation season.
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Senior Scientist
Rob Van Kirk, Ph.D.
P.O. Box 550
Ashton, ID 83420
208-652-3567 OFFICE
208-881-3407 CELL
208-652-3568 FAX
Dr. Rob Van Kirk’s water report of February 18th for the the Henry’s Fork drainage is below.
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Mean temperature yesterday was 3 degrees F below average. Light precipitation was recorded at scattered locations, averaging 0.04 inch over the watershed. The water-year total stayed at 90% of average, but snow water equivalent (SWE) dropped to 75% of average. Current SWE is fifth lowest for the date in the 1989-2021 record, ahead of 1991, 1994, 2001, and 2010. April-1 SWE in those other four years ranged from 59% of average in 2001 to 85% of average in 1991.
All signs point to a similar outcome this year. After light to moderate snow on Sunday and Monday, very cold but dry conditions are expected next week and into the first week of March. The new seasonal outlook for March-May issued yesterday calls for drought conditions to persist. Our best-case scenario this year is a snowpack about like last year’s, in the 80-85% of average range. However, when combined with near record-low stream base flows this winter, water supply will definitely be lower than it was last year.
Reservoirs continue to fill slowly but steadily. Island Park Reservoir is 83% full, compared with 77% full on average. Henry’s Lake is 90% full and very close to average. The upper Snake River reservoir system is 45% full, compared with 64% full on average. Even with above-average precipitation over the remainder of the winter, snowpack will not be sufficient to fill the upper Snake system.
Rob Van Kirk, Ph.D.
Senior Scientist
P.O. Box 550
Ashton, ID 83420
208-652-3567 OFFICE
208-881-3407 CELL
208-652-3568 FAX
Excerpts from Dr. Rob Van Kirk’s February 24th Henry’s Fork water supply report are below.
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Mean temperature last week was 2 degrees F above average, and yesterday’s watershed-average maximum temperature of 39 degrees was the warmest since December 4. Last week was as dry as any in the current dry spell, now in its sixth week. Precipitation was recorded at only four of the 12 stations, amounting to only a few hundredths of one inch when averaged across the watershed. This dropped water-year precipitation from 96% of average last week to 92% of average this morning. In the bigger picture, the three-year running average precipitation, which is a good measure of overall drought conditions at a scale relevant for ecological process and long-term water supply, dropped from just a fraction of an inch below average in early January to 2.5 inches below average over the past five weeks.
The figures for snow water equivalent (SWE) are even worse. Net accumulation of new SWE over the week was 0, dropping SWE from 81% of average to 77% of average over the week. If we have average SWE accumulation between now and early April, this year’s snowpack will end up around 20% below average. At best, we could barely hit average if the remainder of the winter is extremely wet. In the 1989-2021 record, only two years—2011 and 1989—were wet enough between February 14 and April 8 to push this year’s snowpack up to average. That’s only two observed scenarios in the past 33 years, giving us roughly a 6% chance of getting to average in the modern climatic regime.
Weather forecasts and climate outlooks at all scales have not only performed poorly over the past month but have become highly variable from day to day over the past week. Forecasts for this week went from wet a week ago to dry by the end of last week to wet again this morning. Widespread precipitation is expected tonight and tomorrow, followed by moderate chances over the remainder of the week. More widespread precipitation is expected again next weekend. The current 7-day quantitative precipitation forecast is the best it has looked in over a month, calling for widespread amounts of 0.25 inch in the valleys to over 1 inch along the Wyoming border. However, confidence is low past Wednesday of this week. Nonetheless, we will see at least some change from persistent high pressure.
Since Wednesday’s 20-cfs reduction in outflow from Island Park Reservoir, fill rate has averaged 233 ac-ft/day, up from 150-190 ac-ft/day over most of the past five weeks. The reservoir is 82% full, compared with 76% on average. If precipitation over the next week materializes as predicted, gain will be enhanced by about 50 ac-ft/day due to direct precipitation. Outflow has averaged 217 cfs since December 1.
Rob Van Kirk, Ph.D.
Senior Scientist
P.O. Box 550
Ashton, ID 83420
208-652-3567 OFFICE
208-881-3407 CELL
208-652-3568 FAX