This week the weather has changed very rapidly from cool, cloudy and wet with below normal temperatures to hit, dry and above normal temperatures. The result is a major change in stream flow dynamics. Until a few days ago the biggest complaint from anglers fishing the Box Canyon / Last Chance area was low flows.
This past winter and spring were unlike any that I can remember. Our snowpack started out in good shape. By early January it was near normal. However we get most of our snowpack in February, March and early April. This year we had none, zilch, nada. By the end of April the average snowpack in Island Park was less than 50%. Complicating the issue was hot, dry weather the entire month of April. It was great for fishing our early spring hatches and turkey hunting but it started the irrigation season a month early. With such great planting weather farmers put in their crops a month earlier than normal. By the first of May we were in dire straits with the anticipation of drained reservoirs by the end of the summer. Then the rains came.
May brought a reprieve with at least three weeks of solid wet rainy weather. The wet weather alleviated irrigation demand. With the Island Park Reservoir at capacity the flow from the dam was cut to match inflow. That’s why the flow was so low in late May and early June. However, now that it has quit raining and turned hot and dry the demand for irrigation water has quickly outstripped the supply. Normally there is plenty of natural flow from the Henry’s Fork, Fall River and other tributaries to meet irrigation demand without the need for storage water from the reservoirs. That is not the case this year. For example, the normal flow at the gauging station on the Upper Fall River is about 1700 cfs. As of this date it is 270 cfs and continuing to drop. It normally doesn’t get down to 270 cfs at this station until July 12, exactly a month away. This water has to be made up from somewhere.
Fortunately, all of the reservoirs in the irrigation system were filled to capacity. Water has been released in higher volumes from Palisades and Island Park Reservoirs over the past few days. The flow on the South Fork has stabilized for the time being at 16,500 cfs but that could change. The story on the Henry’s Fork is more complex. The flow from the Island Park Dam started to increase a few days ago from 370 cfs to the present flow of more than 800 cfs. We expect this to continue until it reaches at least 1000 cfs. The streamflow at St. Anthony has stayed near 1000 cfs in spite of the rapid increase in streamflow from Island Park. Flows of 1000 cfs or less can be critical for health of the river.
The situation could be even worse if not for the Teton River. It has remained well above normal helping to provide more irrigation water. We expect this to change over the days ahead. As of this writing the flow on the Upper Teton has peaked and started back down. The flow from the Hebgen Lake Dam on the Madison River has gone into a tailspin going from well above normal less than a week ago to well below normal today.
What does all of this have to do with fishing you ask? The answer is everything. We’ve already seen our early bugs like the Salmonfly, Golden Stone, caddis, and PMDs start several weeks earlier than normal. We’ve expected the same from Green Drakes, Flavs and other hatches on the Henry’s Fork as well as the Salmonfly hatch on the Madison and the South Fork. Higher flows will help slow things down on the upper river but the Green Drakes and Flavs are well under way on the Lower Henry’s Fork. Lower Flows should also accelerate the hatches on the Madison. Predicting hatches is far from an exact science but we expect the Salmonflies to start on the Madison by the 20th of the month. They might happen that early on the South Fork but it is hard to say now that the flows are above normal.
One thing for certain, higher flows out of Island Park will bode well for the opening day of the Harriman State Park on June 15th. The flows have been below normal on opening day the past few years resulting in spotty fishing. Look for good hatches of PMDs and caddisflies. We have also been expecting Green Drakes and if the flow stabilizes they should start coming off within the next few days. They are already well under way on the Lower Henry’s Fork, the Upper Henry’s Fork and the Buffalo River. Brown Drakes are also emerging in the evening hours above Coffee Pot Rapids and the Buffalo River.
We are also anticipating great fishing on the Teton River. It has been out of sorts due to all of the rain in May and early June but it is quickly shaping up. Look for PMDs in the upper river and stoneflies and caddisflies lower down.
As far as a report on how the fishing has been over the past 10 days. Take a look at the photos.