Take a tour of the Big Thompson Watershed from the Big Thompson River’s headwaters in Rocky Mountain National Park through the Big Thompson Canyon to Loveland and Greeley.
Rocky Mountain National Park
Within the boundaries of Rocky Mountain National Park are the headwaters—or beginnings—of two large river systems important to Colorado. The Colorado River has its beginnings on the west side of the park, and the Cache la Poudre, Big Thompson, and St. Vrain rivers are headwaters of the South Platte River to the east.
In Rocky Mountain National Park, up to 80% of the annual moisture supply begins as snow during the winter and then melts in the spring to fill rivers, lakes, and reservoirs. Mountain snowfall provides water for recreation, irrigation, municipal, and industrial purposes. Rocky Mountain National Park also protects the Big Thompson’s headwaters from development, preserving the river’s value as a source of clean water.
Lake Estes – Town of Estes Park
Lake Estes was created in 1948 when the Bureau of Reclamation completed construction of Olympus Dam, a feature of the Colorado-Big Thompson (C-BT) Project. Located on the Big Thompson River, the primary purpose of Lake Estes is to store C-BT water diverted from the Colorado River headwaters to the drier plains of northeastern Colorado.
Lake Estes and the surrounding property are owned by the U.S. Through an agreement between the Bureau of Reclamation and the Estes Valley Recreation & Parks District, lands around the lake are managed for a variety of purposes, including recreation, wildlife viewing and habitat, and wetlands.
Town of Drake
The beauty of the Big Thompson Canyon is evident in the Drake area, where the North Fork and Big Thompson rivers meet. During the past 100 years, many areas that were once rural and pristine have been developed for residential and commercial ventures. Individual residences, motels, campgrounds, and other commercial facilities dot the riverfront areas along stretches of the Big Thompson River.
The Drake area is a good example of a canyon watershed area being used for many different purposes. But sometimes, mother nature takes over—such as during the floods of 1976 and 2013. After the 2013 Big Thompson flood, the river reverted to its natural course at its confluence with the North Fork near the town of Drake.
Viestenz-Smith Mountain Park
Since 1925, northern Colorado residents and visitors alike have enjoyed outdoor recreation on the banks of the Big Thompson River in Viestenz-Smith Mountain Park. However, the 2013 flood destroyed all the park’s infrastructure, including the vehicular/pedestrian bridge, parking lot, sidewalks, playground, and picnic areas. As part of the flood restoration efforts in Big Thompson Canyon, the City of Loveland worked to restore the park, including the expansion of recreation opportunities on the north bank of the river out of the floodway, and the park re-opened in September 2018.
The thin green line of life that we find where land meets water is called the riparian zone. The unique environment of the riparian zone supports a specialized wildlife community. You will find plants and animals—like the willow, the kingfisher, and the beaver—that have body parts and habits that help them thrive in the riparian area. Look for the willow’s thick mass of strong roots, the kingfisher’s strong beak, and the beaver’s webbed feet. You can also see cottonwood trees that only grow along the water, ducks dabbling in the shallows, and raccoons using their hands to feel under water for treats. Since all animals drink water several times a day, this is a good place to find upland animals—like rabbits, bighorn sheep, and great horned owls.
The Dam Store and the Colorado-Big Thompson Project
As you enter the Big Thompson Canyon near the Dam Store, you can’t miss the large green pipe that stretches across Highway 34. This is the Big Thompson Siphon, a transmountain water diversion project known as the Colorado-Big Thompson (CB-T) Project. The C-BT system spans 150 miles from east to west and 65 miles from north to south. It is one of the largest water diversion projects of its kind (in acres irrigated), second only to California’s Central Valley Project.
Construction of the CB-T began in 1938 and was completed in 1957. The project diverts water from Colorado’s western slope to the drier eastern slope and plains, delivering an annual average of 220,000 acre-feet of water to 30 cities and towns in northern Colorado to be used for agricultural, municipal, and industrial needs. Water supplied to reservoir and ditch companies helps irrigate more than 600,000 acres of farmland and augments drinking water supplies for more than half a million people.
Detailed map of the Colorado – Big Thompson System
Loveland Visitors Center
Agriculture uses a large portion of the water in the Big Thompson River. In the 1920s, Larimer County farmers grew sugar beets, pinto beans, wheat, corn, barley, and alfalfa. They also cultivated fruit, such as apples, strawberries, and raspberries, and in the early 1900s Larimer County produced two-thirds of Colorado’s total cherry crop.
Today, very few fruit crops are grown in Larimer County on a commercial basis. Instead, the emphasis is on corn, sugar beets, pinto beans, brewing barley, wheat, and alfalfa hay. Producers must have a source of high-quality water to grow these crops.
Greeley and Eastern Plains
Heading east from Loveland, the Big Thompson River crosses the plains into Weld County and joins the South Platte River about five miles south of Greeley. Approximately four miles upstream of its confluence with the South Platte, the Big Thompson receives one of its key tributaries—the Little Thompson River.
As the Big Thompson River flows from the higher elevations to the relatively flat landscape of the eastern plains, it transitions from colder water to a warm water river. While the river’s upper portion has a fish community that includes brook, brown, and cutthroat trout, the lower portion (below Big Thompson Canyon) has a minimal number of trout and is characterized by warm water fish species, such as the plains killifish.