The spring discharges nearly 156 million gallons of water a day at a constant 54°F, welling up through limestone right at the edge of the Missouri. Lewis and Clark stopped here on 18 June 1805 and Clark sketched it in his journal. Today the spring is the centrepiece of a state park with a fish hatchery, picnic area, and easy paved paths along the river.
The Roe River, which emerges from the spring and tumbles a few yards into the Missouri, is one of the contenders for shortest river in the world. Trout swim visibly through the clear water of the spring pool. Combine the visit with a walk to nearby Rainbow Falls overlook for a fuller picture of the river Lewis and Clark struggled around.