The Big Lost River Valley is surrounded by Idaho's tallest, most inhospitable mountain peaks in an area that is ten degrees colder than any other place in the state. It's no place to call home, but the Big Lost has a large population of rainbow trout. It's well worth a visit.

The Big Lost's headwaters, including the East and North forks, begin in Copper Basin, a large circular valley surrounded by incredible mountain peaks 40 minutes east of Ketchum over Trail Creek Pass.

The North Fork survives as a put-and-take fishery, but the East Fork is managed for wild trout and offers some incredible insect hatches and rainbows over 20 inches. There are also brook and cutthroat trout present in smaller numbers.

The East and North forks merge to form the Big Lost River. Trail Creek Road runs parallel to the river and offers easy access at several bridge crossings.

The Big Lost slows at Mackay Reservoir, where you can find some decent rainbows in the 12- to 18-inch range.

Below the reservoir, the river takes on a tailwater nature with all the trimmings, massive insect hatches and wary trout included. The best fishing is located above the town of Mackay. Below Mackay, quality fishing ceases due to irrigation demands.

Accessing the river can be difficult. During late spring and early summer, when the Big Lost typically rips past its banks, dense brush and private lands force you to remain in the river. If you're not a strong wader and are not partial to a skid along the bottom rocks, skip the tailwater section and move to the headwaters, where open sagebrush flats offer easy access and prime casting conditions.

Both the spectacular headwaters area and the tailwater section below Mackay Reservoir have lots of insects and some large rainbows. The Big Lost's rainbows are partial to emerging insects. Use patterns that sit low in the surface film (a Sparkle Dun or a cripple imitation).

Look for Baetis mayflies and midges during the river's winter season, November 30 through March 31. The Baetis should also be present when the stream re-opens in late May. In June and July, you may encounter golden stoneflies, PMDs, Green Drakes, craneflies, and caddis. In August and September, the Big Lost's rainbows turn on to hoppers before returning to a diet of Baetis and midges in October and November.

"The hatches on the East Fork are unbelievable during late June and July as runoff subsides, and that is probably the best time to fish the river," Schnebly says. "The Green Drake emergence is particularly bountiful, and there are good hatches of caddis and Yellow Sallies, too."