It is June 20, 2015 and there is joy in the community of Last Chance, Idaho.
At the access on the north boundary of Harriman Ranch dozens of vehicles fill the large parking area before the giant, white tent that appears at this location each year at this time. They belong to a large gathering of fly fishers that represents booming business for local merchants who rely on the Henry’s Fork for their livelihood. Also benefitting from this enthusiastic group is the Henry’s Fork Foundation, which conducts its annual fund raising event beneath the massive canvas canopy.
All seems well for the Henry’s Fork at this point in the season, and a smile generally describes the expression on the faces of visitors and locals alike. Fishing on all popular sections has been considered good for more than a month and most signs point to a continuation of this trend through a new summer season.
Most prominent in this general sense of optimism is the expectation of favorable water conditions due to Island Park Reservoir being filled to capacity by way of timely spring precipitation and thrift in the way water has been released downstream.
Unfortunately, all that was positive through most of June began to take a different turn as the end of the month drew near.
It is common knowledge that peak agricultural demand for water occurs in July and August. Historically, anglers have understood and accepted that flows from Box Canyon through Pine Haven will be higher than may be completely comfortable during this period. Rarely, however, does the fishing through this most spotlighted section become so disrupted by high water as in 2015.
Flows below 1,200 cfs are not known to severely impact hatches and trout behavior as applied to the dry fly fishing for which the Henry’s Fork is internationally known. However, when flows exceed 1,200 cfs, which is about average inmost years, problems begin to appear. This applies especially to wading anglers who may become limited to fishing the edges or extremely wide sections like Bonefish Flat where depth does not often become prohibited.
It is also understood that unusually hot and dry weather can dictate that more water from the reservoir will be needed for crop irrigation downstream. We who live here accept this as an unchangeable reality for a working river like the Henry’s Fork. What is not understood is why in a month of below average temperature and near average precipitation were flows during the month of July more reflective of a withering draught rather than a normal summer month.
With flows peaking at 1,800 cfs and averaging around 1,500 cfs, the last week of June through the first three weeks of July saw a mass migration of disappointed and frustrated anglers from a swollen Henry’s Fork to friendlier waters like the South Fork of the Snake or the Missouri in Montana.
Most who remained on the Henry’s Fork found themselves compressed into limited and isolated areas where concentrated numbers of trout were available. Particularly victimized by the significantly altered condition of the river were visitors who arrived without warning or preparation to deal with a shortage of rising trout and water largely inaccessible to the wading angler. But it was not elevated water levels alone that produced such a grim scene on the beloved river.
I have never known exceptionally high water levels to be of long term detriment to the river but when accompanied by significant quantities of silt, it is a different story. And unfortunately, this is what occurred during the high flows that marked most of the month of July. arcity of rising trout at this time is undoubtedly more related to a serious reduction in water quality brought on by a troubling entry of sediment from Island Park Reservoir.
By itself, extremely high water represents only temporary disruption to the fly fisher. A tall water column almost always results in the shifting of a trout’s attention to subsurface food forms. For fans of the dry fly, this means fewer targets even though the fish may be feeding ravenously on the underwater forms of a prominent hatch. Unfortunately, however, the scarcity of rising trout at this time is undoubtedly more related to a serious reduction in water quality brought on by a troubling entry of sediment from Island Park Reservoir.
I have never known exceptionally high water levels to be of long term detriment to the river but when accompanied by significant quantities of silt, it is a different story. And unfortunately, this is what occurred during the high flows that marked most of the month of July.
Depending on the volume of water being released from the reservoir visibility into the water varied from one to two feet until July 20, and then it got worse.
On July 21, an announced increase that essentially doubled the flows of 1210 cfs from the previous day brought visibility into the water to zero, and the river became a veritable monster for the next three days.
Explained as being needed for testing turbines at the Chester Dam Hydro facility about 35 miles downstream, the highest releases from Island Park Reservoir in more than 20 years caused the water at Last Chance to resemble heavily creamed coffee. And while water clarity had noticeably improved by the third day, the river remained deserted throughout the period.
Mercifully, flows became somewhat normalized at just below 1,000 cfs on July 24. And more importantly, sediment movement into the river became instantly reduced when water exiting from the reservoir was routed exclusively through the hydro plant.
While the relatively brief reliving of the disastrous siltation event of the early 1990’s resurrected painful memories, the river appears to have weathered the storm without catastrophic effect. However, it will take some time for conditions to stabilize with respect to the level of impact on aquatic hatches and the trout population. These and other questions should be answered in the near future, but this difficult time for the Henry’s Fork cannot be trivialized.
The public deserves believable explanations and authentic damage assessment related to a very disturbing chain of events. There can be no question that problems exist behind Island Park Dam. Silt is an enemy of a healthy fishery, and this reality cannot be ignored.