Henry’s Fork, August 15th, 2023

Water Quality Information from  Dr. Rob Van Kirk’s 8/14  HF drainage report

Water quality was good to excellent over the weekend, although afternoon high water temperatures have crept up a little over the past few days. However, afternoon highs have exceeded 70 degrees only at Buffalo River, St. Anthony and Parker, and then by lower margins than earlier in the summer. Mean daily water temperatures have been close to average at all locations. Dissolved oxygen concentrations have been good to excellent at all locations, benefiting from both cooler mean water temperatures (cooler water can hold more oxygen) and continued high photosynthesis from aquatic vegetation. Aquatic productivity is very high right now but not at the expense of high water temperatures and low dissolved oxygen.

In part as a result of Friday’s outflow decrease and in part because of improving water quality in the reservoir, turbidity at Island Park Dam has decreased by 1-1.5 Nephelometric Turbidity Units (NTU) since then and was below average over the weekend. Turbidity at Pinehaven is near the lowest we have recorded this time of year.

All in all, streamflow, water quality, and aquatic ecosystem productivity are about as good as they can get throughout the whole watershed right now. With another round of cooler, wetter weather expected next week, I anticipate conditions to remain excellent for another two weeks.

• Rob Van Kirk, Ph.D.
• Senior Scientist
• Henry’s Fork Foundation
• P.O. Box 550
• Ashton, ID 83420

Patterns for Grass Hoppers are Effective During Summer Days

• Same as our last report: Best fishing success is during AM spinner falls and trico emergences. Then again as evening approaches through using long drag-free drifts of hopper or flying ant patterns each accompanied by a small dropper of your favorite nymph pattern.