Mackay Reservoir Fishing Guides
A high valley reservoir on the Big Lost River under the Lost River Range, stocked for trout and fished from boats in summer and through the ice in winter.
Guides on the Mackay Reservoir
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About the Mackay Reservoir
Mackay Reservoir impounds the Big Lost River in the broad high valley between the Lost River and White Knob ranges, with Borah Peak and the highest ground in Idaho standing directly above it. It is a working irrigation reservoir rather than a natural lake, and everything about how it fishes follows from that. The pool is full in early summer and drawn down steadily through the irrigation season, so the same water can look like a substantial lake in June and something considerably smaller by September. Anglers who know the reservoir plan around that cycle rather than being surprised by it.
The fishery is a stocked trout fishery with wild fish moving in from the river. Rainbow trout are the mainstay and are planted regularly, Yellowstone cutthroat and brook trout come down out of the Big Lost drainage, and mountain whitefish are common. Kokanee have been part of the mix as well. Fishing is straightforward: trolling and still fishing from small boats through the open-water months, and ice fishing through the winter, which in a valley this high and this cold is a long and dependable season. The reservoir is not a trophy water and does not pretend to be, but it produces steady catches in a setting that is hard to beat.
The Big Lost River below the dam is a separate and well-regarded trout fishery in its own right, and many trips to the area combine the two. The USGS gauge at the reservoir reports stage, and reading it before a trip tells you most of what you need to know about ramp usability and how much water you will actually find. Access is easy, with a state-managed recreation site and a highway running along the valley, and the town of Mackay immediately downstream supplies the basics. Services are limited in this part of Idaho, so arriving supplied is the sensible approach.
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Access
Mackay - the small town just downstream of the dam, with basic services and the nearest supplies.
Mackay Reservoir Recreation Site - the developed access on the reservoir, with a ramp and camping.
Big Lost River below the dam - a separate and well-regarded trout fishery reached from the highway.
Chilly - the small settlement up the valley to the northwest.
Arco - the nearest town to the southeast, with fuel and lodging.
Lost River Range - the mountain front immediately east, including Borah Peak.
Idaho Falls - the closest city of size, well to the southeast.
Seasons
Spring: ice comes off late at this elevation and the reservoir fills with snowmelt, which is when the pool is at its best and the trout fishing opens up.
Summer: the main boating season, with the pool dropping steadily as irrigation demand draws it down through July and August.
Fall: low water and cold nights, with fishing concentrated in whatever depth remains and the river below the dam often the better option.
Winter: a long, cold and reliable ice fishing season in a valley that freezes hard and stays frozen.
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Questions
What species can you catch on the Mackay Reservoir?
Anglers target Brook Trout, Kokanee Salmon, Mountain Whitefish, Rainbow Trout, Yellowstone Cutthroat Trout on the Mackay Reservoir in Idaho.
Where can you access the Mackay Reservoir?
Mackay - the small town just downstream of the dam, with basic services and the nearest supplies. Mackay Reservoir Recreation Site - the developed access on the reservoir, with a ramp and camping. Big Lost River below the dam - a separate and well-regarded trout fishery reached from the highway. Chilly - the small settlement up the valley to the northwest. Arco - the nearest town to the southeast, with fuel and lodging. Lost River Range - the mountain front immediately east, including Borah Peak. Idaho Falls - the closest city of size, well to the southeast.
When is the best time to fish the Mackay Reservoir?
Spring: ice comes off late at this elevation and the reservoir fills with snowmelt, which is when the pool is at its best and the trout fishing opens up. Summer: the main boating season, with the pool dropping steadily as irrigation demand draws it down through July and August. Fall: low water and cold nights, with fishing concentrated in whatever depth remains and the river below the dam often the better option. Winter: a long, cold and reliable ice fishing season in a valley that freezes hard and stays frozen.
Where are the fishing regulations for the Mackay Reservoir?
Regulations change by season and section. Read the current rules on the Idaho agency site: https://idfg.idaho.gov/rules/fish