Lost streams of Idaho

They are often considered separate streams, but both flow into the same depression and become subterranean, feeding the Snake River Aquifer.

A dam impounds the river and creates Mackay Reservoir.

The sinks and the lower courses of both rivers are within the land of the Idaho National Laboratory, northeast of Craters of the Moon.

The Big Lost River's drainage basin is approximately 1,400 square miles (3,626 km2) in area[2] Its mean annual discharge, as measured by USGS gage 13132500 (Big Lost River near Arco), is 91.7 cubic feet per second (2.60 m3/s), with a maximum daily recorded flow of 1,840 cu ft/s (52 m3/s), and a minimum of zero flow.

[3] The Little Lost River's drainage basin is approximately 971 square miles (2,515 km2) in area[2] Its mean annual discharge, as measured by USGS gage 13118700 (Little Lost River below Wet Creek, near Howe, Idaho), is 65 cubic feet per second (1.8 m3/s), with a maximum daily recorded flow of 486 cu ft/s (14 m3/s), and a minimum of 3 cu ft/s (0.085 m3/s).