Hot Days and High Water

For good reason, June is the month chosen by many fly fishers for a visit to the Henry’s Fork.

Consistently would describe the primary elements that June typically brings to the fortunes of those who probe the fertile waters of the world renown trout stream. This applies in particular to hatches that have attained legendary status for their ability to generate dry fly opportunity, which sets the Henry’s Fork apart from most other waters. In this respect, the past month has delivered timely appearance of the famed Green Drakes and other notable attractions spread across a remarkably wide spectrum of aquatic insect types.

This year, the prosperity derived from the assortment of mayflies, caddis, and stoneflies extended through the most prominent sections of the river from its upper reaches in Island Park to St. Anthony, about forty-five miles downstream. But that consistency with June norms reached an end when weather entered the picture.

Deviating from the general trend of moderate temperatures and fairly frequent rain, June twenty-one saw highs frequently reaching ten to fifteen degrees above daily average and precipitation fell more than 50 % below normal. With these extremes, it was no surprise when a declaration of drought was issued to include Henry’s Fork country and nearly all of the Rocky Mountain region.

With management of the Henry’s Fork structured mainly for the benefit of irrigation of downstream cropland, it is understandable that June streamflow would experience considerable instability as the result of questionable water supply for the summer growing season.

Established in the interest of preserving water stored in Island Park Reservoir, release into the river was limited to three hundred cfs or less from May through mid-June, which produced a water level little more than knee-deep through Last Chance Run during that period.

It was just prior to the June fifteen opening of Harriman Ranch that flows began to increase, and that trend has continued since that point. Fifteen hundred cfs is a flow almost unheard of at this early date. But with sustained temperatures pushing record highs this was the release level from Island Park Dam as June came to an end. Problematic if not perilous now describes wading the river in some parts where the depth is waist deep or more, and the possibility of even higher flows is very real.

With no change in the hot, dry weather pattern in sight and thirsty potatoes continuing their demand for more water than usual, expect to be dealing with uncomfortable temperatures and higher flows for the foreseeable future.

While troublesome sediment entering the river is associated with larger release from the reservoir, there is an upside to the extreme water level currently flowing in the Henry’s Fork that is not present on some rivers where the drought will result in dangerously low water levels as summer progresses.

More water in the river means that the Henry’s Fork trout population will not be as severely affected by excessively high-water temperature that comes with inadequate streamflow.

Moving forward, I will plan to be on the water earlier and remain there later to avoid the discomfort and disruption of extreme mid-day heat. I will also plan to work a little harder to overcome the slight level of hostility presented by recent limitations of wading a normally friendly river.


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