The Big Lost River

21 March 2006 By Dan Bachman • Fishing-Spots • Comments (3)

The Big Lost below the Mackay Reservoir runs through the town of Mackay towards Arco. With just 2 weeks left in the winter fishing season I drove nearly 4 hours from Eagle last weekend to visit this tailwater. And I’m glad I did.

With flow rates at just over 100 CFS the resident rainbows are feeding heartily while gearing up for the spawn and the water is low and clear—a surefire formula for fishing nirvana.

View from Willow Creek Summit looking towards Mackay.  Temperature was a balmy 24 degrees at 7:30 A.M. Big Lost below Mackay Reservoir

Getting access to the river can be a little tricky due to the fact that so much of the river is surrounded by private land as it runs southeast below the dam. I opted for one of the Sportsman’s Access points that is wedged among the ranch and farm land.

A careful survey of the river when I arrived at 9:00 showed no surface activity. The temperature was right at freezing and with the sun peaking from behind clouds I new that it wouldn’t be long before midges would appear.

While stringing up my rod I met a couple “local” anglers including Randy Flynn, a fly tier from Hailey. As I waited impatiently for the hatch to begin, Randy invited me to come nymph with him. He had a massive fly box around his neck that looked like it was heavy enough to act as a boat anchor. He pulled out a couple midge nymphs that were nothing more than red string wrapped around the shank of a #18 hook. He guaranteed my success with the pattern as I moved downstream where I tied it on below a strike indicator.

Randy Flynn, fly tier from Hailey, ID, fishing a riffle Successful flies (left to right on enlarged photo) 1. Midge Larvae courtesy of Randy Flynn  2. Trico CDC Biot Thorax.  3. CDC Hanging Midge

The wind begin to blow bitterly as I cast to a riffle near the top of the pool where I had immediate success. The nymph pattern that can’t possibly take more than 20 seconds each to tie, brought me 2 nice rainbows before I began to notice the gentle “bloop” sound of rising fish.

Looking downstream I could see a half-dozen or so fish that were pulling naturals from the surface. That was all I needed to stash the nymph and tie on a hanging midge pattern from my own fly box.

While moving into position above the first rising fish I crossed a thin water flat where I saw the biggest fish of the day move from just above the beginning of a riffle. As he swam to a submerged tree at the opposite bank the dorsal and tail fin broke the surface and were a good 10 inches apart putting the length of the fish at 20+ inches. Anxious to get to a fish that I could easily see I had missed one that I should have seen.

My consolation prize was a very fiesty 16 inch rainbow that I took on the second down and across cast. The coloration on The Big Lost rainbows is something that you need to see to believe. The brilliant salmon red band along the sides was only outdone by the black spotting. I have never seen rainbows with so many spots on the head and on the lower belly. (Compare to a Silver Creek Rainbow shown here)

Hold the rod in one hand and take a picture with the other... A 16 incher

As I caught my 4th or 5th fish the hatch was at the stage that Tim Burke from The River Keeper Fly Shop would call a “freak show”. At one point I didn’t know which fish to cast to next. The one rising 7-8 feet upstream seemed too easy. But. How can you resist? Fish were on nearly every other cast during one 45 minute stretch.

One of these days I will take a pic with the fish in the air... Smile for your closeup

The day wasn’t without its challenges though. The wind caused considerable troubles with casting at different times. And I lost feeling in the tips of a couple of my finger tips at one point making it almost impossible to tie on size 20 flies. Finally, parts of the river are very closed in by trees that I am sure hold a treasure trove of lost flies.

With only 10 days left in the winter fishing season you’d better get a move on it if you don’t want to miss out. And be careful to avoid the redds in the river if you do. I spotted one and it’s just about that time of the year.

Map of Big Lost River

Take care to avoid the redds when fishing this time of year Author with a rainbow



  1. 23 March 2006 Craig

    Awesome report thanks for the update I wish I had a day that I could run up there during spring break next week.

  2. 24 March 2006 Don

    Great Rport, and that pic of the rainbow in the water is cracking, its a skill holding the rod while trying to focus on a fish with a camera you dont want to drop in the water

  3. 24 March 2006 Author

    Don-not to mention that it took 5 or 6 shots to get the one that you see. Glad you like the pic.

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