Big Lost River
Runs from the Pioneer Mountains into Mackay Reservoir, south through farm valley past Arco, then out onto the Snake River Plain where it disappears into the ground at the Sinks.
Course of the river, simplified. Map data from Natural Earth (public domain).
Weather at the Big Lost River (National Weather Service) ↗
River facts
| Length | About 135 miles |
|---|---|
| Source | North and East Forks meet, Pioneer Mountains, Custer County, Idaho |
| Mouth | Big Lost River Sinks, Butte County, Idaho (sinks underground) |
| State | Idaho |
A dam near Mackay forms Mackay Reservoir.
Boat ramps, launches and bait shops
Detailed ramp, bait shop and lock-and-dam listings for the Big Lost River are coming soon. Until then, these searches open Google Maps along the river:
Fishing regulations
Check the state agency for river-specific rules, seasons and limits before you fish:
Lakes on or near the Big Lost River
Lakes in our guide on or near this river:
Facts from Big Lost River (Wikipedia) ↗