Henry’s Fork, May 4th, 2024
Flow is down throughout the river thanks to our recent surprise snow storm (maybe more to come next week), So note what Dr Rob Van Kirk says below about development of aquatic insect growth in his water quality discussion below.. Nevertheless the lower river continues to offer the best stream fishing in the area with great BWO, mother’s day caddis, and midge activity bringing trout up from the bottom. If water quality stays decent and warms a bit, stonefly nymphs will soon wake up. All boat launch locations on the lower river are open.
Headlines from Dr. Rob Van Kirk’s SWE Report for the Henry’s Fork Drainage Filed Yesterday, May 4th
- Another cool, showery day kept water-year total precipitation at average and kept SWE constant at 83% of this season’s peak, compared with 87% of peak on average.
- Very cold, wet weather is expected Sunday–Wednesday, which will add snowpack and likely put SWE near average for the date by the middle of next week.
- Natural flow dropped for the fourth consecutive day and was 83% of average yesterday.
- Water temperatures increased a little yesterday but were still below average, continuing to slow aquatic organism development.
Water Quality 5/3/ 24
Water quality remains very good in all river reaches, as dissolved oxygen concentrations are high and turbidity continues to drop after last week’s peak streamflows. Water temperatures were a hair warmer yesterday than on Wednesday but still below average. Yesterday’s temperatures were generally below the optimal range for development of rainbow trout eggs and fry, which is not harmful but just slows development. Similarly, aquatic insect development continues to slow, as I had predicted at the end of last week. Current hatch timing is within a day of average at most locations but will drop to a day or two behind average by the middle of next week.
In absence of a managed freshet flow out of Island Park Reservoir, sediment mobilization and transport out of the Island Park-to-Pinehaven reach has been below average so far this spring, despite streamflow last week that was almost as high as last year’s managed freshet. In fact, yesterday’s net export of sediment from the reach was the lowest for the date in the 8 years we have measured that quantity carefully. There are two primary reasons for that: 1) there is relatively little fine sediment in that reach to transport this year after last year’s highly successful springtime freshet and subsequent low export of sediment out of the reservoir last summer, and 2) as we learned from last year’s freshet compared with previous freshets, rapid increase in outflow mobilized much more sediment than gradual increase, even if the magnitude ended up about the same. I expect relatively low sediment export rates to continue throughout the remainder of the period before aquatic vegetation growth really gets underway.
Rob Van Kirk, Ph.D.
Senior Scientist
P.O. Box 550
Ashton, ID 83420
208-881-3407 CELL