The 10 Longest Rivers in the U.S.: From the Missouri to the Brazos

Determining the exact length of a river is complicated, and figuring out the longest river in the U.S. is no exception. To start, there’s the question of whether or not the river’s tributaries should be included. That can be tough, as the beginning or end points of tributaries are not always easy to define.

Even the United States Geological Survey (USGS) acknowledges that “somewhat arbitrary decisions” are made, often relying on maps, aerial photos, and other factors when measuring the lengths of rivers.

When the USGS set out to list the country’s most significant rivers, it measured each one’s “total length from source to mouth.” Based on this standard, the agency identified the following 10 rivers as the longest in the United States.

1. The Missouri River

There’s debate over whether the Missouri or Mississippi holds the title of longest river in the U.S., but according to the USGS, the Missouri takes the lead by 200 miles (322 km), with a total length of 2,540 miles (4,088 km) from its source to its mouth.

The Missouri River begins in the Rocky Mountains, flowing through seven states—Montana, North Dakota, South Dakota, Nebraska, Iowa, Kansas, and Missouri—before joining the Mississippi River near St. Louis.

The Missouri River’s watershed covers more than 525,000 square miles (845,000 square km), nourishing local ecosystems. The Blackfeet, Crow, and other Native American groups lived along the upper Missouri for centuries. This river was also the route taken by explorers Lewis and Clark before they reached the Columbia River and continued to the Pacific Ocean.

2. The Mighty Mississippi River

The iconic Mississippi River, spanning a massive 2,340 miles (3,766 km), is often regarded as the longest or second-longest river in the U.S., depending on your measuring methods.

What’s universally agreed upon, however, is that the Mississippi is one of the world's largest rivers, boasting the U.S.'s most extensive drainage area. Its basin covers 31 states and extends over an astounding 1.2 million square miles (3.1 million square km), roughly one-eighth of North America.

Some experts even place the Mississippi River system among the longest rivers globally. Once a boundary between the American West and the rest of the country, it flows from Minnesota through 10 states, ultimately reaching the Gulf of Mexico.

3. The Majestic Yukon River

The mighty Yukon River, which originates in the Pelly Mountains of Canada's Yukon Territory in British Columbia, travels a vast 1,980 miles (3,187 km) through Alaska's untamed terrain before flowing into the Bering Sea.

Covering a vast area of 328,000 square miles (52,865 square km), the Yukon River's drainage basin is larger than the entire country of Turkey, stretching across both the Canadian province and Alaskan wilderness.

As it journeys toward the Bering Sea, the Yukon River serves as a crucial transportation route, linking remote villages and supplying vital resources such as salmon and fresh water.

4. The Rio Grande

Flowing a distance of 1,900 miles (3,058 km), the Rio Grande, known as 'El Rio Grande' in Spanish, acts as a natural boundary between the United States and Mexico. It begins in Colorado's San Juan Mountains, travels through New Mexico and Texas, and empties into the Gulf of Mexico, with a watershed of 336,000 square miles (540,740 square km).

The Rio Grande River has sculpted remarkable canyons along its path, including the striking Santa Elena Canyon in Texas, renowned for its towering limestone cliffs and breathtaking vistas. However, its erratic flow has placed it at the heart of ongoing disputes between the U.S. and Mexico over water rights and the allocation of water for agricultural lands and municipalities.

5. The Arkansas River

The Arkansas River begins its journey in the Rocky Mountains of Colorado, near the Continental Divide, and travels 1,469 miles (2,364 km) through Kansas and Oklahoma before converging with the Mississippi River in Arkansas.

Famed as one of the premier whitewater rafting spots in the United States, the Arkansas River draws adventure enthusiasts from all over who seek to tackle its exhilarating rapids, including the renowned Royal Gorge section. Its watershed spans 161,000 square miles (259,104 square km).

6. The Colorado River

The Colorado River, stretching 1,450 miles (2,334 km), is famous for two major reasons. It is responsible for carving the magnificent Grand Canyon over millennia, and it has several dams along its course, the most famous being the Hoover Dam.

Covering a watershed area of 246,000 square miles (637,000 square km), the Colorado River is a vital water and hydropower resource for major cities such as Los Angeles, Las Vegas, and Phoenix. Its hydroelectric capacity supplies power to over 40 million people across seven U.S. states and Mexico.

Originating in the Rocky Mountains, the Colorado River meanders westward and southward, eventually reaching the Gulf of California and the Pacific Ocean. Uniquely, it is the only river in this list that flows toward the Pacific.

7. The Atchafalaya River

The Atchafalaya River, which stretches for 1,420 miles (2,285 km), including the Red River, plays a crucial role in preserving the unique ecosystems of Louisiana. It diverges from the Mississippi River near Simmesport, Louisiana, and flows toward the Gulf of Mexico, effectively serving as a natural flood control mechanism.

The combination of flood control measures implemented by the U.S. Army Corps of Engineers and other solutions helps reduce the risk of severe flooding in areas downstream. Spanning a watershed of 95,100 square miles (246,300 square km), the river's basin is home to the largest floodplain swamp in North America.

8. The Ohio River

The Ohio River, which begins where the Allegheny and Monongahela Rivers converge in Pittsburgh, Pennsylvania, flows 1,310 miles (2,108 km). It is the largest tributary to the Mississippi River and has a vast watershed area of 203,000 square miles (326,697 square km).

Several rivers, such as the Tennessee River, Cumberland River, and Kanawha River, contribute to the flow of the Ohio. In addition to Pittsburgh, major cities like Cincinnati, Ohio, and Louisville, Kentucky, are located along its banks.

9. The Red River

The Red River begins in New Mexico and travels through the Great Plains, passing through Texas, Oklahoma, Arkansas, and Louisiana. It eventually merges with the Mississippi River, covering a total distance of 1,290 miles (2,076 km). For approximately 640 miles (1,030 km), it also serves as the border between Texas and Oklahoma.

The Red River's drainage basin is estimated to cover 93,200 square miles (149,991 square km). However, due to the presence of numerous dams and reservoirs along its tributaries, the flow of the river across the Great Plains can fluctuate significantly depending on the time and source.

10. The Brazos River

The Brazos River, which stretches for 1,280 miles (2,060 km), ranks as the tenth longest river in the U.S. and is the longest river that flows entirely within Texas. It originates in the Texas panhandle and winds its way through the heart of the state before reaching the Gulf of Mexico.

The Brazos River's length slightly surpasses that of the Columbia River, which spans 1,240 miles (1,996 km) as it flows from British Columbia in Canada through the Pacific Northwest to the Pacific Ocean.

The Brazos River, which has been dammed at several locations to form reservoirs such as Lake Possum Kingdom and Lake Whitney, has a watershed area of 45,600 square miles (7,339 square km). Originally, the river was named Brazos de Dios, meaning 'Arms of God' in Spanish.