Lakes and inland seas

Detail

Basic terms

• Lake: a large body of water that sits in a hollow in the land and has land all around it.
• Inland sea: a very large lake that has salt water, or a sea that is almost cut off from the ocean (e.g. the Caspian).
• Endorheic (closed) basin: a basin with no outlet to the ocean. Water leaves only by evaporation, so salts build up and the lake turns saline. Examples: Caspian, Aral, Dead Sea, Great Salt Lake, Lake Chad.
• Rift lake: a long, deep lake that forms in a rift valley. A rift valley is a strip of land that sinks between two parallel faults (cracks in the crust) when the crust is pulled apart. Examples: Baikal, Tanganyika, Malawi.
• Reservoir: an artificial lake made when a dam blocks a river (e.g. Lake Volta).

North America — the Great Lakes

• Great Lakes: five connected freshwater lakes on the USA–Canada border in east-central North America.
• Mnemonic HOMES: Huron, Ontario, Michigan, Erie, Superior.

• Order from west to east (the way the water flows): Superior → Michigan / Huron → Erie → Ontario.

• Size: together they cover about 244,106 sq km. This is the largest surface of fresh water in the world [5].

• Share of fresh water: the Great Lakes basin holds about 95% of North America's fresh surface water and about 18% of the world's (USGS 2005) [6].
• People: the basin is shared by 2 countries, 8 US states and 1 Canadian province (Ontario). More than 40 million people depend on it for home and industrial water (USGS 2005) [6].
• Key facts:
• Lake Michigan is the only one of the five that lies wholly in the USA.
• Lake Superior is the largest freshwater lake by area, at about 82,100 sq km [5].

• Niagara Falls is on the Niagara River, which joins Lake Erie to Lake Ontario.

• Drainage and shipping:

• The lakes drain into the Atlantic through the St Lawrence River.
• The St Lawrence Seaway (opened 1959) is a system of locks and canals. It lets ocean ships sail into the interior of the continent.
• The International Joint Commission (a USA–Canada body) manages the boundary waters together.

Other North American lakes	Location	Key fact
Great Salt Lake	Utah, USA	Salty lake in a closed basin; a leftover of the Ice Age Lake Bonneville
Great Bear Lake	Northwest Territories, Canada	Largest lake wholly inside Canada; crossed by the Arctic Circle
Great Slave Lake	Northwest Territories, Canada	Deepest lake in North America (about 614 m); the Mackenzie River flows out of it

Asia — the Caspian Sea

• Caspian Sea: the world's largest inland water body, about 371,000 sq km.
• It is a saltwater lake in a closed basin, about 28 m below sea level.
• Bordering countries (5 littoral states): Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan.

• Water supply: the Volga brings most of its water. The Ural and Kura rivers also flow in.

• Resources: oil and gas (Baku in Azerbaijan, Kazakh fields), and sturgeon, the fish whose eggs are sold as caviar.

• Legal status:
• Why it mattered: if the Caspian is a "sea", the UN law of the sea divides it. If it is a "lake", the five states divide it equally.

• Outcome: the five states signed the Aktau Convention (2018), which gives the Caspian a special status of its own.

• Falling level: the water level is dropping. Causes: less water from the Volga and more evaporation as the climate warms.

Asia — Lake Baikal

• Location: a rift lake in south-eastern Siberia, Russia, just north of Mongolia.
• Records:
• Oldest lake in the world, about 25 million years old [2].
• Deepest lake in the world, about 1,700 m according to UNESCO [2] (NCERT: about 1,642 m).

• It holds about 20% of the world's unfrozen fresh water [2].

• World Heritage Site (1996): UNESCO listed it as the most outstanding example of a freshwater ecosystem, under natural criteria (vii), (viii), (ix) and (x). The protected property covers 3.15 million hectares [2].

• Biodiversity:
• It is called the "Galapagos of Russia". Its great age and isolation have produced unusual wildlife [2].
• It has about 1,340 animal species (745 endemic) and 570 plant species (150 endemic) [2]. Endemic means found nowhere else.
• It is home to the nerpa (Baikal seal), one of the few seals that live only in fresh water.

Asia — Aral Sea (a human-made disaster)

• Location: on the Kazakhstan–Uzbekistan border. It was once about 68,000 sq km, the 4th-largest lake in the world [3].
• What went wrong:
• Cause: from the 1960s, Soviet projects took water from the Amu Darya and Syr Darya rivers to irrigate cotton fields.
• Process: less river water reached the sea, so evaporation became greater than inflow.

• Result: the sea is now only about 10% of its 1960 size [3]. It has split into the North Aral (Kazakhstan) and the South Aral [4].

• Effects: the dry seabed has become the Aralkum, a toxic desert. Winds carry salt and pesticide dust from it. Fishing towns collapsed.

• Partial recovery:
• Kazakhstan's Kok-Aral Dam (completed 2005) holds back water in the North Aral. It replaced an earlier dike from the 1990s [4].
• By 2011, the North Aral's salinity was back to its 1960s level of about 8 g per litre, and its fisheries have recovered [4].
• Trade-off: the dam lets less water flow on, so the South Aral keeps shrinking and getting saltier [3][4].

Asia and South America — other lakes

Lake	Location	Key fact
Balkhash	Kazakhstan	The west half is fresh because the Ili River flows in. The east half is salty. A narrow strait joins the two
Dead Sea	Jordan–Israel/West Bank	Lowest point on land (about 430 m below sea level); very salty, about 34%; a closed basin fed by the Jordan River
Titicaca	Peru–Bolivia, Andes (Altiplano)	At about 3,812 m, the highest large navigable lake

Africa — Lake Victoria

• Records: Africa's largest lake (about 68,800 sq km), the world's largest tropical lake, and the second-largest freshwater lake by area after Superior.
• Countries: Uganda, Kenya and Tanzania. It sits on a plateau between the two arms of the East African Rift. It is not a rift lake.
• Nile link: it is the main source of the White Nile, which leaves the lake at Jinja, Uganda.
• Invasive species: an invasive species is a non-native species that spreads and harms local life.
• Nile perch was brought in during the 1950s. It is a large predator fish and ate hundreds of native cichlid fish species, many to extinction.
• Water hyacinth is a floating weed that blocks sunlight and oxygen and chokes boats and fishing.

Africa — Rift lakes

Lake	Countries	Key fact
Tanganyika	Tanzania, DR Congo, Burundi, Zambia	Longest freshwater lake (about 670 km) and second deepest (about 1,470 m), after Baikal; lies in the Western Rift
Malawi (Nyasa)	Malawi, Mozambique, Tanzania	South of Tanganyika, at the southern end of the Western Rift; has a very large number of cichlid fish species

Africa — Lake Chad

• Location: a shallow lake in the Sahel (the dry belt south of the Sahara). It is shared by Chad, Cameroon, Niger and Nigeria.
• Shrinking:
• It has shrunk by more than 90% since the 1960s: from about 25,000 sq km in 1963 to under 1,500 sq km in 2001 [7].
• Main cause: less rain in the Central African Republic, where its main feeder rivers, the Chari and Logone, begin [7].

• Other causes: repeated droughts and irrigation that takes river water.

• Effects:

• Hunger: fishing, farming and herding failed, and people became food insecure.
• Conflict: poverty and joblessness helped Boko Haram grow, and people were forced from their homes.
• Response: the World Bank's PROLAC project (2020s) works to restore livelihoods and resilience around the lake [8].

Africa — Lake Volta

• Lake Volta (Ghana) is a reservoir. The Akosombo Dam on the Volta River (1965) created it. It is one of the largest reservoirs in the world by area.

Prelims Hooks

• HOMES = Huron, Ontario, Michigan, Erie, Superior. Michigan is the only one wholly in the USA.
• Niagara Falls lies between Erie and Ontario. The Great Lakes drain to the Atlantic through the St Lawrence (Seaway opened 1959).
• Largest inland water body: Caspian. Largest freshwater lake by area: Superior. Deepest and oldest: Baikal. Longest freshwater lake: Tanganyika.
• Depth order, deepest first: Baikal > Tanganyika > Malawi.
• Lake–river pairs: Caspian–Volga; Aral–Amu Darya and Syr Darya; Balkhash–Ili; Victoria–White Nile (outflow); Chad–Chari and Logone; Great Slave–Mackenzie (outflow).
• Trap: Lake Victoria is not a rift lake. Tanganyika, Malawi and Baikal are.
• Trap: Balkhash is half fresh (west) and half salty (east).
• Kok-Aral Dam (2005) saved the North Aral (Kazakhstan), not the South Aral.
• Aktau Convention (2018) deals with the legal status of the Caspian Sea.
• Lake Baikal became a World Heritage Site in 1996. Its endemic seal is the nerpa.

Mains Points

• Human-made drying (GS-I/III): the Aral Sea (cotton irrigation) and Lake Chad (drought plus irrigation) both shrank by about 90%.
• Effects: toxic dust storms, collapse of fisheries, falling health, migration, and conflict (Boko Haram).

• Lesson for India: manage whole river basins and the demand for water, not just supply. Examples to watch: shrinking lakes such as Sambhar and Loktak.

• Recovery is possible but involves trade-offs: the Kok-Aral Dam brought back fish and lowered salinity in the North Aral, but the South Aral was given up. Restoration often has to choose which part to save.

• Shared lakes need shared rules: the Caspian (Aktau Convention 2018), the Great Lakes (International Joint Commission) and the Lake Chad Basin Commission show how countries sharing a lake can manage it together. This is useful for India's shared river waters.
• Threats to lake biodiversity (GS-III): invasive species in Lake Victoria (Nile perch, water hyacinth) and pollution threats to Baikal. Compare water hyacinth in Indian wetlands and the Ramsar Convention's approach.