Global Rivers and Freshwater Lakes

Rivers are natural channels of flowing fresh water that drain land toward an ocean, a sea or a lake, and freshwater lakes are large bodies of standing fresh water in basins on the land. In brief: the longest rivers are the Nile and the Amazon (each roughly 6,400–6,650 km, depending on how they are measured); the Amazon carries by far the largest volume of water. The largest freshwater lake by area is Lake Superior, and the deepest and largest by volume is Lake Baikal in Siberia. Rivers and lakes supply drinking water, irrigation, energy, transport and fisheries, and have shaped the location of many civilizations.

The world’s rivers and lakes hold only a small fraction of Earth’s fresh water, but they are the most accessible source for people. This guide describes the major rivers and lakes, compares them in a table, works through discharge and volume calculations, outlines their role in history and corrects common mistakes.

What are the major rivers?

• Nile (Africa): about 6,650 km, flowing north from East Africa to the Mediterranean through Sudan and Egypt; the Aswan High Dam, completed in 1970, regulates its flow.
• Amazon (South America): about 6,400 km (some measurements are longer), with the largest drainage basin and discharge of any river, about 209,000 m³ per second, which is roughly a fifth of the fresh water that all rivers deliver to the oceans.
• Yangtze (Asia): about 6,300 km, the longest river in Asia, flowing from the Tibetan Plateau to the East China Sea; the Three Gorges Dam is on it.
• Mississippi–Missouri (North America): about 6,300 km, draining the center of the United States to the Gulf of Mexico.
• Others: the Yenisei and Ob in Siberia, the Yellow River (Huang He) in China, the Congo (the deepest river and second in discharge), the Mekong, the Ganges–Brahmaputra, the Indus, the Danube and the Rhine in Europe, and the Murray–Darling in Australia.

The length of a river depends on where the source is considered to be and how the channel is measured, so the ranking of the Nile and the Amazon is disputed. A river basin (drainage basin or watershed) is all the land drained by a river and its tributaries.

What are the major freshwater lakes?

The five Great Lakes of North America (Superior, Michigan, Huron, Erie and Ontario) together form the largest group of fresh water lakes, and Lake Superior (about 82,100 km²) is the largest freshwater lake by surface area. Lake Victoria in East Africa (about 59,900 km²) is the largest in Africa and the main reservoir of the Nile’s White Nile branch. Lake Baikal in Siberia is the deepest lake in the world (about 1,640 m) and contains roughly 20 percent of the unfrozen surface fresh water. Lake Tanganyika in Africa is the second deepest and the longest freshwater lake. The Caspian Sea is the largest lake of all (about 371,000 km²), but its water is salty, not fresh. Lakes may be formed by tectonic movement (Baikal, Tanganyika), glaciers (the Great Lakes), volcanoes (crater lakes), or river action (oxbow lakes).

Why do rivers and lakes matter?

They provide drinking water, irrigation for farming, hydroelectric power, inland transport, fish, and recreation. Fertile floodplains and deltas are among the most productive farmland. They also create challenges: floods, pollution, over-extraction, dams that change flows and sediments, and disputes between countries sharing a river (the Nile, the Mekong, the Danube). Lakes, such as the Aral Sea (which has largely dried up after rivers were diverted for irrigation), can change rapidly when water is overused.

Rivers and lakes compared

Worked example: discharge and volume

1. Amazon discharge per day: 209,000 m³/s × 86,400 s = 18.06 billion m³, or 18.1 km³ per day (1 km³ = 10⁹ m³).
2. Amazon discharge per year: 18.06 × 365 = about 6,590 km³ per year.
3. Nile and Amazon lengths: the difference between 6,650 and 6,400 km is 250 km, which is 250 ÷ 6,650 = 3.8 percent, which is within the uncertainty of how the source and the course are defined, and explains why the ranking is disputed.
4. Baikal and Superior volumes: Baikal holds about 23,600 km³ and Superior about 12,100 km³; 23,600 ÷ 12,100 = 1.95, so Baikal contains nearly twice as much water, even though its area (about 31,500 km²) is smaller than that of Superior, because it is far deeper.
5. Lake areas: Superior is 82,100 ÷ 59,900 = 1.37 times as large as Victoria in area.
6. Mean depth check for Baikal: volume ÷ area = 23,600 km³ ÷ 31,500 km² = 0.75 km = about 750 m.

How have rivers and lakes shaped history?

The early civilizations of Mesopotamia (Tigris and Euphrates), Egypt (Nile), the Indus Valley and China (Yellow River) grew along rivers that provided water, silt and transport. The Great Lakes and the Mississippi were routes for exploration and trade in North America, and the Rhine and Danube served as transport corridors and frontiers in Europe. Dams and canals have been built for millennia; in the 20th century, large dams such as the Aswan and the Hoover Dam produced electricity, controlled floods and, at the same time, changed ecosystems and displaced people.

Which mistakes are common?

Mistake 1: Giving one definite answer for the longest river

The Nile and the Amazon are close in length, and the answer depends on the measurement.

Mistake 2: Confusing length with volume of water

The Amazon carries many times more water than the Nile, though the Nile may be longer.

Mistake 3: Calling the Caspian Sea a freshwater lake

It is salty, with about a third of the salinity of the ocean.

Mistake 4: Mixing up area with volume for lakes

Lake Superior has the largest area among freshwater lakes, but Baikal holds more water because of its depth.