Fishing Reports

Henry’s Fork, July 22nd, 2023

The Tubs

Water Quality Information from Dr. Rob Van Kirk’s Henry’s Fork Drainage Report Filed Yesterday.

Water quality continues to exceed expectations throughout the watershed, especially given hot dry weather and very high reservoir outflow. Water temperatures yesterday were a little cooler than on Wednesday due to cloud cover and close to average. Afternoon high water temperatures exceeded 70 degrees at our usual warm spots—Buffalo River, Pinehaven, St. Anthony, and Parker—but the duration and magnitude of temperatures greater than 70 degrees was lower than on Wednesday. Water temperatures stayed within the optimal range of 53–68 degrees all day at all of our other sonde locations. Dissolved oxygen continues to stay good to excellent—and above the state cold-water standard of 6 mg/L—at all locations.

Turbidity is still well below average at all locations between Island Park Dam and St. Anthony and among the lowest readings we have observed during mid-July since first installing our water-quality network in 2014. This is despite outflow through Island Park Dam gates higher than we have seen this time of year since 2013. The common denominators among the years with lowest turbidity—2017, 2018, 2019, and 2023—are near- to above-average snowpack and high Island Park Reservoir levels.

Timing of aquatic insect hatches is still around 5 days later than average in the river reach between Island Park Dam and Pinehaven, 8 days later in the Warm River to Ashton reach, and 4 days later than average between Ashton Dam and St. Anthony.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

There are a few comments on why we continue to place Dr. Rob’s observations on the fishing report. We do so because many of these give reasons for fly fishing success. They also help in deciding where and when to try your luck on drainage waters.

Consider that although aquatic insect hatches remain a bit late in much of the drainage, terrestrial insect populations are building and are becoming quite important as a trout food along the entire river and its tributaries.

Henry’s Fork, July 18th, 2023

With the warming weather and bright skies up and down the river, it is time for terrestrial insects to become an important food form for trout.. That means long, drag free drifts in front of well vegetated banks and dry structure such as snags, rocks and logs. Have hopper, ant, beetle, and even crane fly patterns on hand.

A productive trick follows: I swat any horsefly that lands on my self, then toss the splatted results into the water to drift downstream. On hearing or seeing a trout rise to take it, I have located another fish to try. Do the same with hoppers or any other resident terrestrial insect to locate a feeding fish. You might be accused by your fishing partners of low grade chumming, but the act is legal and informative!

Henry’s Fork at Bear Gulch

Water quality information from Dr. Rob Van Kirk’s Henry’s Fork drainage water status report filed yesterday.

The big (positive) story continues to be how well water quality is holding up so far this summer, despite high outflow from Island Park Reservoir and warm weather. Water temperatures have stayed near average and well below last year’s readings at most locations. Daily maximum water temperatures exceeded 70 degrees yesterday at Buffalo River, Pinehaven, at St. Anthony and Parker. However, both duration and magnitude of high water temperatures are lower than at this time last year. For example, water temperature exceeded 70 degrees at Pinehaven yesterday for a little under 6 hours yesterday, compared with 7.5 hours on July 16 2022. Maximum water temperature yesterday was 71.8 degrees F at our sonde, compared with 72.9 degrees last July 16.

Turbidity is well below average at all locations except Flat Rock, where relatively high outflow from Henry’s Lake has kept turbidity a fraction of a turbidity unit above average.

Timing of aquatic insect hatches is still 5–6 days later than average in the river reach between Island Park Dam and Pinehaven, 8 days later in the Warm River to Ashton reach, and 4 days later than average between Ashton Dam and St. Anthony. At this point, I do not expect much change with respect to average.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Henry’s Fork, July 15th, 2023

Flav

The river below Ashton Dam is beginning to warm to the point that best fishing is early or late in the day. Big stonefly activity and the same for drake mayflies is about over. Afternoon caddis action remains , and PMD and flav spinner falls at these times of day will bring some top water action. Streamers can also be effective when direct sun light is off the water. Big bows and browns come out to forage at these times because of increased overhead cover.

After the July 10th increase in flow out of Island Park Dam, conditions have stabilized in the river below. Brown drake, flav, little PMD, and afternoon caddis activity still provide top water fishing with AM spinner falls and evening action. Expect recreational floaters to increase during day time hours.