It is sometimes difficult to measure the true length of a river due to certain factors: the source, the mouth, scale of measurement, whether measured by the center or the edge, seasonal or annual changes that alter the water.

Then there are factors such as flooding, dams, levees, and channelization that can change the length of a river. 

The following is a list of the longest rivers (in order of length) in the world, by continent, based on approximations.

1. Nile River (Africa)

By Rod Waddington, CC BY-SA 2.0, Link

The Nile River is a major north-flowing river in northeastern Africa that flows into the Mediterranean Sea.

For some time, there was a dispute between the Nile or the Amazon being the longest river in the world.

The latest reports show that the Nile is the longest river in the world. It is 4,404 miles (7,088 km) long.

Its drainage covers eleven countries and is the primary water source of Egypt, Sudan and South Sudan.

2. Amazon River (South America)

The Amazon River is the largest river by discharge volume of water in the world, and the disputed longest river in the world.

The Amazon represents 20% of the global riverine discharge into oceans, with a basin area of approximately 7,000,000 km² (2,700,000 sq miles). Its length is 4,345 miles (6,992 km). 

3. Yangtze River (Asia)

CC BY 2.0, Link

The Yangtze River is the longest river in Asia. It flows entirely into one Country, China.

It rises in the Tanggula Mountains and flows in an easterly direction to the East China Sea.

It has the seventh-largest river by discharge volume in the world, comprising one-fifth of the land area of China. It is 3,988 miles (6,418 km) long.

4. Mississippi River (North America)

The Mississippi River flows from its traditional source of Lake Itaska in northern Minnesota south to the Mississippi River Delta in the Gulf of Mexico.

The Mississippi’s watershed drains all or parts of 32 U.S. states and two Canadian provinces between the Rocky and Appalachian mountains.

It’s 3,902 miles (6,275 km) long. 

5. Yenisey River (Europe)

The river as seen from the trans-Siberian railway near Krasnoyarsk
Link

The Yenisey River has the largest drain into the Arctic Ocean. Rising in Mungaragiyn-gol in Mongolia, it follows a northerly course before draining into the Yenisey Gulf in the Kara Sea.

The Yenisey divides the Western Siberian Plain in the west from the Central Siberian Plateau to the east and drains a large part of central Siberia.

It’s 3,445 miles (5,539 km) long. 

6. Murray River (Australia)

The Murray River is actually the 16th longest river in the world, but the longest one in Australia.

Its tributaries include five of the next six longest rivers of Australia and cover about one-seventh of the continent.

It is 2,282 miles (3,672 km) long.

7. Onyx River (Antarctica)

Onyx River flowing into Lake Vanda
Link

The Onyx River is the longest river in Antarctica. At only 20 miles (32 km) long, the stream flows westward through the Wright Valley from the Wright Lower glacier and Lake Brownworth at the foot of the glacier to Lake Vanda.

That happens during the few months of the Antarctic summer. Flow levels are variable, during the day and between summers, so much so that the river fails to reach the lake some years. 

Other Notable Rivers

• Yellow River in Asia — 3,395 miles (5,464 km) long
• Ob-Irtysh in Asia — 3,364 miles (5,410 km) long
• Rio de la Plata River in South America — 3,030 miles (4,880 km) long
• Congo River in Africa — 2,922 miles (4,700 km) long
• Amur River in Asia — 2,763 miles (4,444 km) long
• Lena River in Asia — 2,736 miles (4,400 km) long
• Mekong River in Asia — 2,705 miles (4,350 km) long
• Mackenzie River in North America — 2,637 miles (4,241 km) long
• Niger River in Africa — 2,611 miles (4,200 km) long
• Brahmaputra River in Asia — 2,466 miles (3,969 km) long