Big Spring Creek flows out of Big Spring, the third-largest freshwater spring in the world, pumping 50,000 gallons per minute. One of the cleanest streams in the U.S., Big Spring serves as Lewistown's unpurified municipal drinking water supply and as a source for several brands of commercial bottled water. The creek runs approximately 30 miles from the Big Springs Trout Hatchery at its headwater through Lewistown before joining the Judith River northwest of town.
The Big Springs Trout Hatchery, seven miles southeast of Lewiston, is the largest coldwater hatchery in Montana, producing up to 130,000 pounds of fish annually to stock some 100 Montana waters with rainbows, Yellowstone cutthroats, brown trout, and Kokanee salmon
Montana Fish, Wildlife & Parks maintains six seasonal public fishing access sites along Big Spring Creek. Caddis hatch January through mid-September; Pale Morning Dun July through August; and Baetis March through May.