Henry’s Fork, September 6th, 2022
Visits to the upper river are decreasing significantly, and presenting terrestrial insect patterns is the best way to find daytime fishing success. Speckled dun and caddis activity provide lesser daytime action while tricos bring on early in the day action before increasing air temps awaken terrestrial insects. With shorter daylight hours and colder nights, water in the lower river will begin to cool to the point that fall may lfy activity will begin.
Headlines from Dr. Rob Van Kirk’s Henry’s Fork drainage status report of yesterday follow. :
- High temperature records were broken on five of the last six days, and dry weather has dropped water-year total precipitation to 90% of average.
- Natural streamflow and diversion have dropped very slowly over the past few days.
- Outflow from Henrys Lake was decreased on Saturday, so Island Park Reservoir is now dropping at around 1000 ac-ft/day at 970 cfs outflow.
- Water quality: Because of warm water temperatures in Island Park Reservoir, dissolved oxygen concentration dropped over the weekend, necessitating transfer of some outflow from the power plant back to the gates. That caused a slight increase in turbidity, but it remains near or below average at all locations in the watershed. Despite hot air temperatures, shorter day length and lower sun angle have kept water temperatures out of the stressful range at all locations, as expected. Afternoon high water temperatures have dropped steadily at all locations for the past four days and stayed below 70 degrees at all locations yesterday. Water temperature at Pinehaven has stayed below 68 degrees for the past four days. Expect water temperatures to continue to drop incrementally over the next two days and then more substantially as cooler weather arrives later in the week.
Rob Van Kirk, Ph.D.
Senior Scientist
P.O. Box 550
Ashton, ID 83420
208-881-3407 CELL
208-652-3568 FAX