Fly Fishing the Big Lost River Tailwater

The Big Lost River is a freestone stream with its headwaters located in the Pioneer Mountains of Central Idaho. The Big Lost River quickly leaves the big steep canyon and flows into Big Lost Valley providing spectacular scenery as it wanders from Aroco through the wild west town of Mackay and further to Willow Creek Summit.

From the Lost River Valley the Pioneer Mountains and the Lost River Mountains can be seen with several mountains in the 11,000 foot to 12,000 foot elevations creating some of the best scenery in the Rocky Mountains. Wildlife is in abundance, with Pronghorn Antelope and Elk dominating the scenery. 

The North Fork and the East Fork are combined to form the main stem of the Big Lost River. The North Fork is a small stocked stream while the East Fork is small stream with wild trout and is protected with some special regulations. The trout are primarily rainbows with a few cutthroat trout. 

However, that portion of the Big Lost River that leaves the McKay Reservoir as a tailrace is somewhat remote and often overlooked by anglers. The Reservoir is small and the tailwater is small as well averaging only about 20 to 30 feet wide and the banks are lined with cottonwood trees. There are plenty of overhanging bushes along the banks often making landing a big trout a challenge. 

Wild rainbows averaging 15 to 20 inches and more are what make the Big Lost River Tailwaters so interesting. The McKay Reservoir is full early in the spring and the releases into the Big Lost River can be frequent and high, but in the summer the water becomes more suitable for fishing. 

Fishing the Lost River Tailwaters: 

The releases from the dam depends on the snow pack and will in some years cause the tailwater to remain high until mid June or even the first of July.  As soon as the water recedes to a lower level of around 175 cfs, it is time to do some sight fishing for trout. You can expect the river to become crystal clear and light gear will be the order of the day. Fish with 7X tippet, stay hidden and make your first cast your best presentation.

Spring: 

Late winter and early spring fishing will be good with hatches of the blue winged olives occurring from November until May. Midges are the other hatches that occur and imitations of the larva, pupa and adult stages will all work.  Also, streamers can be used and the big rainbows will hit streamers hard. However, the spring is the least favorite time to fish this river. Winter can be a time to consider only if the weather is warm and the releases are favorable so be sure to check them. November 1^st to March 31^st is catch and release only. 

Summer:

The caddis, pale morning duns, and little yellow stoneflies hatches will be underway by late may continuing through June and fishing can become absolutely super once the water releases from Mackay reservoir are cut back, and wading becomes possible. From the middle of June through the middle of July, the salmonfly nymphs will be moving toward the banks to hatch and the nymoh patterns will be successful. Some serious stalking and sight fishing combined with small dry flies and nymphs will surely yield some nice rainbows. 

Fall:

The autumn season is probably the best time to fish the Big Lost River since the temperature will be comfortable and the scenery at its peak. The trout will be aggressive as they feed up for winter and it is suggested that a heavier rig will be necessary. During the warmest part of the day, blue winged olive and black baetis in both dry fly and nymph patterns will work. Also, be sure to include some terrestrials to fish among the cottonwood overhangs and use some weighted streamers especially in the the deeper faster water.