A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, tributary and rill; there is no general rule that defines what can be called a river, although in some countries or communities a stream may be defined by its size.

Many names for small rivers are specific to geographic location; one example is “burn” in Scotland and northeast England. Sometimes a river is said to be larger than a creek, but this is not always the case, because of vagueness in the language.

Length (km): 4,444
Length (miles): 2,763
Drainage area (km²): 1,855,000
Average discharge (m³/s): 11,400
Outflow: Sea of Okhotsk
Countries in the drainage basin: Russia, China, Mongolia

The Amur or Heilong River is the world’s tenth longest river, forming the border between the Russian Far East (Outer Manchuria) and Northeastern China (Inner Manchuria).

A river is part of the hydrological cycle. Water within a river is generally collected from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice   and snow pack’s (e.g., from glaciers).Potamology is the scientific study of rivers.

Length (km): 4,700
Length (miles): 2,922
Drainage area (km²): 3,680,000
Average discharge (m³/s): 41,800
Outflow: Atlantic Ocean
Countries in the drainage basin: Democratic Republic of the Congo, Central African Republic, Angola, Republic of the Congo, Tanzania, Cameroon, Zambia, Burundi, Rwanda

Length (km): 4,880
Length (miles): 3,030
Drainage area (km²): 2,582,672
Average discharge (m³/s): 18,000
Outflow: Rio de la Plata
Countries in the drainage basin: Brazil (46.7%), Argentina (27.7%), Paraguay (13.5%), Bolivia (8.3%), Uruguay (3.8%)

The Parana River is a river in south Central South America, running through Brazil, Paraguay and Argentina for some 4,880 kilometers (3,030 mi). It is second in length only to the Amazon River among South American rivers.

Length (km): 5,410
Length (miles): 3,364
Drainage area (km²): 2,990,000
Average discharge (m³/s): 12,800
Outflow: Gulf of Ob
Countries in the drainage basin: Russia, Kazakhstan, China, Mongolia

The Ob River, also Obi, is a major river in western Siberia, Russia and is the country’s fourth longest river. It is the westernmost of the three great Siberian rivers that flow into the Arctic Ocean (the other two being the Lena River and the Yenisei River). The Gulf of Ob is the world’s longest estuary.

Length (km): 5,464
Length (miles): 3,395
Drainage area (km²): 745,000
Average discharge (m³/s): 2,110
Outflow: Bohai Sea
Countries in the drainage basin: China

The Yellow River or Huang He / Hwang Ho is the second-longest river in China (after the Yangtze River) and the sixth-longest in the world at the estimated length of 5,464 kilometers (3,395 mi). Originating in the Bayan Har Mountains in Qinghai Province in western China, it flows through nine provinces of China and empties into the Bohai Sea. The Yellow River basin has an east-west extent of 1900 km (1,180 mi) and a north-south extent of 1100 km (684 mi). Total basin area is 742,443 km² (290,520 mi²).

Length (km): 5,539
Length (miles): 3,445
Drainage area (km²): 2,580,000
Average discharge (m³/s): 19,600
Outflow: Kara Sea
Countries in the drainage basin: Russia (97%), Mongolia (2.9%)

Yenisei, also written as Yenisey, is the greatest river system flowing to the Arctic Ocean. It is the central of the three great Siberian Rivers that flow into the Arctic Ocean (the other two being the Ob River and the Lena River). Rising in Mongolia, it follows a northerly course to the Yenisei Gulf in the Kara Sea, draining a large part of central Siberia, the longest stream following the Yenisei-Angara-Selenga-Ider.

Length (km): 6,275
Length (miles): 3,902
Drainage area (km²): 2,980,000
Average discharge (m³/s): 16,200
Outflow: Gulf of Mexico
Countries in the drainage basin: United States (98.5%), Canada (1.5%)

The Mississippi River is the largest river system in North America. Along with its major tributary, the Missouri River, the river drains all or parts of 31 U.S. states stretching from the Rocky Mountains in the west to the Appalachian Mountains in the east to the Canada–US border on the north, including most of the Great Plains, and is the fourth longest river in the world and the tenth most powerful river in the world.

Length (km): 6,418
Length (miles): 3,988
Drainage area (km²): 1,800,000
Average discharge (m³/s): 31,900
Outflow: East China Sea
Countries in the drainage basin: China

The Yangtze, Yangzi or Chang Jiang is the longest river in Asia, and the third-longest in the world. It flows for 6,418 kilometers (3,988 mi) from the glaciers on the Tibetan Plateau in Qinghai eastward across southwest, central and eastern China before emptying into the East China Sea at Shanghai.

Length (km): 6,400
Length (miles): 3,976
Drainage area (km²): 6,915,000
Average discharge (m³/s): 219,000
Outflow: Atlantic Ocean
Countries in the drainage basin: Brazil, Peru, Bolivia, Colombia, Ecuador, Venezuela, Guyana

Length (km): 6,650
Length (miles): 4,132
Drainage area (km²): 3,349,000
Average discharge (m³/s): 5,100
Outflow: Mediterranean Sea
Countries in the drainage basin: Ethiopia, Eritrea, Sudan, Uganda, Tanzania, Kenya, Rwanda, Burundi, Egypt, Democratic Republic of the Congo

The Nile is a major north-flowing river in North Africa, generally regarded as the longest river in the world.