The Roe River is recognized by the Guinness Book of World Records as the world's shortest river. The Roe flows 200 feet between Giant Springs and the Missouri River near Great Falls. The Roe River competes with the D River in Lincoln City, Oregon for the title of the shortest river. Both rivers have been measured on different occasions, with lengths varying from 58 feet to 200 feet. Schoolchildren in Great Falls campaigned successfully to have the Roe River placed in the Guinness Book of World Records. The source of the Roe River, Giant Springs, is the largest freshwater spring in the United States. Compared to the Roe, the Missouri River is the longest river in the nation.The Roe River and Giant Springs were first explored by Lewis and Clark in 1805 during their Louisiana Purchase expedition. Most of the Roe River runs parallel to the Missouri River, then curves its mouth and feeds its water into the Missouri. The majority of the Roe River is peaceful, with tranquil and quiet water. At the beginning of the Roe River however rests the bubbling and brewing Giant Springs where water flows over large sandstones creating an active, small waterfall effect. Giant Springs is an opening in the Madison Aquifer, a massive freshwater aquifer that underlies five American states and two Canadian provinces. Snow melt water takes almost 2,900 years to travel underground before returning to the surface at the springs. Lewis and Clark came across Giant Springs in 1805. Clark correctly guessed that it was the largest freshwater springs in the world, by volume. It is a beautiful public park today. What you see here is not man-made. It is a natural sedimentary formation that creates a huge pool that the springs wells up in. The springs then overflow into the Missouri River and into the Roe River. At 200 feet (61 m), the Roe River is the shortest river in the world.