|Big Spring, Wonderful Spring, Roe River, North Fork Roe River|
|- location||Great Falls, Cascade County, Montana|
|- elevation||3,314 ft (1,010 m) |
|Length||0.04 mi (0 km)|
|Discharge||for Giant Springs outlet|
|- average||242 cu ft/s (7 m3/s) |
Giant Springs is a large first magnitude spring located near Great Falls, Montana. Its water has a temperature of 54 °F (12 °C) and originates from snowmelt in the Little Belt Mountains, 60 miles (97 km) away. According to chlorofuorocarbon dating, the water takes 26 years to travel underground before returning to the surface at the springs.
Giant Springs is formed by an opening in a part of the Madison aquifer, a vast aquifer underlying 5 U.S. States and 3 Canadian Provinces. The conduit between the mountains and the spring is the geological stratum found in parts of the northwest United States called Madison Limestone. Although some of the underground water from the Little Belt Mountains escapes to form Giant Springs, some stays underground and continues flowing, joining sources from losing streams in the Black Hills, Big Horn Mountains and other areas. The aquifer eventually surfaces in Canada.
The spring outlet is located in Giant Springs State Park, just downstream and northeast of Great Falls, Montana on the east banks of the Missouri River. Giant Springs was discovered by Lewis and Clark during their exploration of the Louisiana Purchase in 1805.
Giant Springs has an average discharge of 242 cubic feet (6.9 m3) of water per second.
Today, some of the spring water is bottled for human consumption, some of the discharge is used for a trout hatchery, and the spring is the headwaters of the 200-foot (61 m)-long Roe River, the shortest river in the world according to Guinness Book of World Records. A Montana state trout hatchery named Giant Springs Trout Hatchery is located here too. The river flows into the Missouri River which is near the spring and borders its state park. Besides the location of a world record holder, Giant Springs is also the most-visited state park in Montana.
- Giant Springs State Park: State of Montana Fish, Wildlife, and Parks
- Giant Springs 1, Great Falls,Montana : 8-25-2010
- Giant Springs 2, Great Falls,Montana : 8-25-2010
- Giant Springs 3, Great Falls,Montana : 8-25-2010