Lakes & Types of Lakes – UPSC

• A lake is a body of relatively still water occupying an enclosed hollow of the land surface, surrounded by land and fed by rivers, rain, groundwater or meltwater.
  • Lakes range from pond-sized tarns of a few square metres to the Caspian Sea (about 3,71,000 km²), the largest inland water body on Earth.
• Lakes are temporary features on the geological time-scale: every lake is born in a basin, fills with sediment or loses its outlet, and is eventually obliterated.
• In geomorphology lakes are studied as landforms of many origins (tectonic, glacial, volcanic, fluvial, aeolian, solution, coastal, mass-movement, biological, impact and human), each leaving a basin of distinctive shape.

Meaning, Distribution and Characteristics

Meaning: Lake and Related Water Bodies

• Not every lake is inland: coastal lakes such as Chilika lie behind sand bars and exchange water with the sea.
• Lakes are best defined by their stillness and enclosure, not by salinity or size.

Water body	Nature	Typical size and depth	Indian example
Lake	Natural, enclosed, still water	Large; deep enough to stratify	Wular, Loktak, Pangong Tso
Pond	Natural or dug; light reaches the bed	Small, shallow	Village ponds of the Ganga plain
Lagoon	Coastal, partly cut off by a bar or reef	Shallow, brackish	Chilika, Pulicat, Vembanad
Reservoir	Artificial lake behind a dam; level regulated	Varies with the dam	Gobind Sagar, Nagarjuna Sagar

Distribution of Lakes

• Lakes occur from the equator to Antarctica and from below sea level to the high plateaux, but they cluster where basins and water supply coincide.
  • Glaciated high latitudes: the lands scoured by the Pleistocene ice sheets are “gardens of lakes“: Canada, Finland, Sweden, Norway and the US Great Lakes region.
  • Rift zones: long, deep lakes of the East African Rift, Baikal and the Dead Sea–Jordan trough.
  • Arid and semi-arid basins: shallow salt lakes and playas of the Great Basin (USA), the Altiplano, Central Asia and the Thar.
  • Floodplains, deltas and coasts: oxbows, beels and lagoons.
• Extremes: the Dead Sea is the lowest lake (about 430 m below sea level and still falling); Titicaca (3,812 m) is the highest navigable large lake; Baikal (1,642 m) is the deepest.
• The world’s largest lakes, the Caspian, Superior, Victoria, Huron and Michigan, are all of tectonic or glacial origin.
• India: the Himalaya are studded with glacial lakes (Roopkund, Gurudongmar, Chandra Tal); the Kumaon lake region holds Naini Tal, Bhim Tal, Sat Tal and Naukuchia Tal; Rajasthan has salt lakes; the east and west coasts have lagoons, so India’s lakes span almost every genetic type.

Characteristics of Lakes

• Two conditions are needed for a lake:
  • A closed depression (basin, trough or hollow) where water can stand.
  • A regular water supply: rainfall, inflowing rivers, meltwater, or groundwater where the water table stands above the basin floor.
• Water budget: inlets bring water in; outlets drain it; the level of the outlet fixes the lake level, and evaporation governs volume in dry climates.
  • Open lakes have outlets and stay fresh; closed (endorheic) lakes lose water only by evaporation and turn saline (Caspian, Dead Sea, Great Salt Lake, Pangong Tso, Sambhar).
• Wide variation in altitude, depth (Baikal over 1.6 km against seasonal pans a few centimetres deep) and area.
• Thermal stratification in deep lakes: a warm epilimnion over a cold hypolimnion, separated by the thermocline; temperate lakes overturn in spring and autumn, recycling nutrients.
• Salinity depends on climate, inlet–outlet balance and seasonal change in volume.
• Each lake has a life-cycle of origin, development and extinction.

Classification of Lakes

On the Basis of Salinity

• Salts weathered from rocks reach lakes by runoff, rivers and seepage; where outflow removes them the lake stays fresh, and where evaporation exceeds inflow they accumulate and the lake turns saline.
• Most present-day salt lakes are shrunken remnants of larger freshwater lakes of wetter Pleistocene times: the Great Salt Lake of Utah is a remnant of Lake Bonneville, and the Nevada salt lakes are remnants of Lake Lahontan.

Class	Salinity and water balance	World examples	Indian examples
Freshwater	Low salts; high inflow and outflow	Baikal, Superior, Victoria	Dal, Wular, Loktak, Kolleru, Naini Tal
Brackish	Mixed fresh and saline water	Caspian, Vistula Lagoon	Chilika, Pulicat, Pangong Tso, Tso Moriri
Saline	Salts concentrated by evaporation; mostly endorheic	Dead Sea, Great Salt Lake, Aral	Sambhar, Didwana, Pachpadra, Tso Kar

• Types of saline lakes by dominant salt:
  • Alkali (soda) lakes: sodium and potassium carbonates; Lake Turkana, Lake Natron, and India’s Lonar.
  • Bitter lakes: sodium sulphate dominant.
  • Borax lakes: rich in borates; Searles Lake (California).
  • Mixed lakes: several salts together.

On the Basis of Permanence

• Perennial lakes hold water all year (Wular, Dal, Baikal).
• Seasonal or ephemeral lakes fill in the wet season and shrink to salt flats in the dry one: playas of the Great Basin and the Thar, and the salt pans around Sambhar.
• Extinct lakes survive only as flats of lake sediment: Sukha Tal (“dry lake”) and Saria Tal near Naini Tal.

On the Basis of Origin

Group	Basin-forming process	Main types	World examples	Indian examples
Tectonic	Faulting, warping, uplift	Rift, fault, sag, relict	Baikal, Tanganyika, Victoria, Caspian	Pangong Tso, Naini Tal
Glacial	Ice erosion and deposition; ice damming	Tarn, rock-basin, ribbon, kettle, moraine-dammed, ice-dammed	Great Lakes, Finnish lakes, Windermere	Roopkund, Chorabari, South Lhonak
Volcanic	Craters, calderas, lava dams	Crater, caldera, lava-dammed	Crater Lake, Toba, Tana	—
Solution (karst)	Solution of limestone	Doline, uvala, polje, cave lakes	Plitvice, Cerknica	—
Aeolian	Deflation; dune blocking	Blowout, interdune, playa	Nebraska Sandhills	Thar playas
Fluvial	River erosion and deposition	Oxbow, plunge pool, delta, fan, floodplain	Mississippi oxbows	Kanwar Tal, Kolleru, beels
Coastal	Spits and bars enclosing sea water	Lagoon, haff	Vistula Lagoon	Chilika, Pulicat, Vembanad
Mass movement	Landslide or mudflow dam	Landslide, mudflow, slump	Sarez, Attabad, San Cristobal	Gohna Tal
Biological and impact	Animal dams; meteorite craters	Beaver, impact	Beaver ponds; Bosumtwi	Lonar
Anthropogenic	Dams, excavation	Reservoir, pit lake, tank	Lake Nasser	Gobind Sagar, Jaisamand

Tectonic (Diastrophic) Lakes

• Diastrophic movements create the largest, deepest and oldest lakes.
• Relict lakes: parts of former seas cut off by uplift; the Caspian is a remnant of the ancient Paratethys sea.
• Crustal warping (sag or synclinal lakes): broad, shallow downwarps; Lake Victoria occupies a sag between the two arms of the East African Rift; Titicaca lies in the tectonic basin of the Altiplano.
  • Anticlinal damming: a rising fold across a river ponds water upstream.

• Fault lakes: water fills the hollow along a fault; sag ponds such as San Andreas Lake line the San Andreas Fault.
  • Pangong Tso occupies a long trough along the Karakoram Fault zone; Naini Tal lies in a fault-controlled depression rather than a cirque.
• Rift valley lakes fill a graben, the block dropped between two parallel normal faults: long, narrow, very deep, floors often below sea level.
  • Baikal is the oldest (25–30 million years) and deepest lake and holds about one-fifth of the world’s unfrozen surface freshwater; its rift is still widening.
  • Tanganyika (about 1,470 m deep) is the second deepest and the longest freshwater lake; the Dead Sea lies in the Jordan rift.

Glacial Lakes

• Glaciers form more lakes than any other agent; most date from the retreat of the Pleistocene ice. The Great Lakes, scoured by the Laurentide ice sheet, show that ice can create even the largest lakes.
• Lakes of glacial erosion, among the erosional glacial landforms:
  • Cirque lakes (tarns): meltwater in the over-deepened floor of a cirque; Roopkund, Hemkund and Sheshnag.
  • Rock-basin lakes: hollows scoured in the valley floor or by ice sheets on shields; Finland (“land of a thousand lakes”).
  • Ribbon (finger) lakes: long, deep lakes in glacial troughs; Windermere and the Finger Lakes of New York. A chain of rock basins down a trough forms paternoster lakes.

• Lakes of glacial deposition:
  • Ground moraine lakes: small, shallow, often outletless ponds in hollows of uneven till left by a retreating ice sheet; thousands dot Canada and Minnesota.
  • Terminal moraine lakes: water held behind or between recessional moraine ridges; Grand Lake (Colorado).
  • Lateral moraine lakes: water ponded where a lateral moraine blocks a tributary valley, or between the moraine and the valley wall.
  • Kettle lakes: hollows left in outwash when buried blocks of stagnant ice melt; small and irregular. Kame lakes form among kame mounds.
  • Drumlin-field lakes occupy waterlogged hollows between drumlins.
• Moraine-dammed lakes of the Himalaya are the main source of glacial lake outburst floods: Chorabari above Kedarnath (2013) and South Lhonak in Sikkim (2023).

• Ice-dammed lakes form where a glacier blocks a valley; they drain catastrophically when the ice dam floats or fails.
  • Pleistocene Lake Missoula and Lake Agassiz in North America; in India, the Chong Kumdan glacier repeatedly dammed the Shyok, with outbursts in the 1920s.
• Periglacial lakes: thermokarst lakes fill hollows left by thawing ground ice in the permafrost of Siberia, Alaska and Canada, and are multiplying as the Arctic warms.

Volcanic Lakes

• Crater lakes fill the vents of dormant or extinct cones, usually with no surface outlet.
• Caldera lakes fill the large basins left when a summit collapses into an emptied magma chamber, a process also called cauldron subsidence; they are the largest volcanic lakes.
  • Crater Lake (Oregon), in the caldera of Mount Mazama, is about 594 m deep, the deepest lake in the USA; Toba (Sumatra) is the largest volcanic lake.
• Lava-dammed lakes: a lava flow solidifies across a valley and ponds the river; Lake Tana (Ethiopia) and Lake Kivu.
• Collapse lakes: the roof of a hollow lava tube or flow collapses, leaving a depression.

Solution (Karst) Lakes

• Rainwater charged with carbon dioxide dissolves limestone into closed hollows; lakes form when their floors are plugged with clay or debris or reach the water table.
  • Doline and uvala lakes in sinkholes; polje lakes, often intermittent, in large flat-floored karst depressions (Lake Cerknica, Slovenia).
  • Cave lakes in underground caverns; collapse of a cave roof exposes long, narrow lakes.
  • Travertine-dammed lakes: the terraced Plitvice Lakes (Croatia), a UNESCO World Heritage Site.
• Solution basins also form in rock salt and gypsum.

Aeolian Lakes

• Deflation (blowout) lakes: wind scoops hollows down to the water table; heavy evaporation turns them into salt lakes, the playas among desert landforms.
  • The Thar has many such saline depressions, locally dhands or ranns: Didwana, Pachpadra and Lunkaransar.
• Sand-dune lakes: dunes block drainage or water collects between dunes; the Nebraska Sandhills and the Badain Jaran desert of China.

Fluvial Lakes

• Rivers are more often destroyers than creators of lakes, because they fill basins with sediment and cut down outlets; lakes among fluvial landforms are small and short-lived.
• Oxbow (horseshoe) lakes: a meandering river cuts across the neck of a loop and the abandoned loop is sealed off.
  • Abundant along the Ganga, Gandak, Ghaghara, Gomti and Kosi; Kanwar (Kabar) Tal in Bihar, a Ramsar site, is a residual oxbow of the Gandak system. Oxbows far from the present channel mark palaeochannels.

• Plunge-pool lakes: in pools scoured at the foot of waterfalls, left behind as falls recede.
• Rock-bar (structural) lakes: a band of resistant rock across a channel ponds the river until it is cut through.
• Floodplain lakes: water in hollows of uneven flood deposits and backswamps behind levees; the chaurs of north Bihar.
• Delta lakes: water trapped between distributaries; Kolleru lies between the Godavari and Krishna deltas; in the Ganga–Brahmaputra delta they are beels; Lake Manzala on the Nile delta.
• Alluvial-fan lakes: fans at mountain feet block streams; small lakes along the Siwalik foothills.
• Raft lakes: log jams dam a channel temporarily, as the Great Raft of the Red River (USA) once did; their failure brings flash floods.

Coastal Lakes

• Spits, bars and barrier islands built by waves and longshore drift cut off shallow, brackish lagoons from the sea; offshore reefs enclose atoll lagoons. These marine landforms are called haffs on the Baltic coast of Germany and Poland.
  • Chilika (Odisha) is India’s largest brackish-water lagoon (about 900–1,165 km²); Pulicat is second; Vembanad, the longest lake in India, and Ashtamudi are Kerala kayals.

Mass-Movement (Barrier) Lakes

• Landslides, rockfalls, screes, avalanches and mudflows dam valleys to form barrier lakes; most are short-lived because loose debris is breached as water builds up, releasing floods.
  • Gohna Tal: a rockslide in 1893 dammed the Birahi Ganga, a tributary of the Alaknanda; the dam burst in August 1894 and swept away Srinagar (Garhwal), but a timely warning kept deaths very low.
  • Attabad Lake (Hunza, Pakistan) formed after the landslide of January 2010; Lake San Cristobal (Colorado) is held by the Slumgullion mudflow.
  • A few survive for centuries: Sarez Lake (Tajikistan), dammed by an earthquake-triggered landslide in 1911.
• Mudflow and slump basins form smaller ponds.

Biological, Impact and Anthropogenic Lakes

• Biological: beavers build dams of timber and mud that create durable ponds and wetlands, making the beaver a keystone species.
• Meteorite impact lakes: Lonar (Buldhana, Maharashtra) fills a crater about 1.8 km wide and 150 m deep, a rare impact crater formed wholly in basalt; it is saline and highly alkaline, and turned pink in June 2020 as low water raised salinity and favoured salt-loving microbes.
• Anthropogenic: reservoirs behind dams (Gobind Sagar on the Sutlej, Nagarjuna Sagar on the Krishna, Umiam in Meghalaya); historic tanks such as Jaisamand (Udaipur); pit lakes in abandoned mines; fishponds and ornamental lakes.

Obliteration and Life-Cycle of Lakes

• A lake passes through youth, maturity and old age, though not every lake completes the sequence.
  • Youth: clear, deep, nutrient-poor (oligotrophic) water; sharp shoreline.
  • Maturity: deltas advance, the basin shallows, nutrients rise (mesotrophic).
  • Old age: nutrient-rich (eutrophic), weed-choked, with marsh encroaching; the lake becomes a swamp, then a meadow (hydrarch succession).
• Most existing lakes are young, formed during or after the Pleistocene glaciation; floodplain and delta lakes are the chief exceptions.

Cause	Process	Example
Siltation	Inflowing rivers build deltas and fill the basin	Himalayan and Kumaon lakes; Wular
Lowering of the outlet	The outflowing stream cuts down and drains the lake	Pleistocene Karewa lake of Kashmir, drained through the Baramulla gorge
Diastrophism	Uplift or tilting of the lake bed	Former Kumaon lakes
Evaporation and climate change	Inflow falls below evaporation	Lake Chad; Pleistocene Lake Bonneville
Eutrophication	Nutrient loading, weed growth, organic infill	Dal, Loktak
Human action	River diversion, reclamation, encroachment	Aral Sea; Kolleru; Bengaluru lakes

• The Aral Sea shows how fast a lake can die: once the fourth-largest lake, it shrank into separate remnants after the Amu Darya and Syr Darya were diverted for irrigation from the 1960s.

Significance of Lakes and Contemporary Indian Issues

Significance of Lakes

• Hydrological: lakes store water and damp floods; Wular absorbs the Jhelum’s floodwater, varying from about 30 to 189 km² through the year.
• Water supply and energy: drinking water (Chennai’s Red Hills and Chembarambakkam lakes), irrigation and hydropower (the Loktak project).
• Climate: large lakes moderate local temperature; the Great Lakes cause lake-effect snow.
• Economy: fisheries (Wular yields about 60% of Kashmir Valley’s fish; Chilika supports over 1.5 lakh fisherfolk), salt from Sambhar, soda, borax and lithium from saline lakes, navigation on the Great Lakes–St Lawrence route, and tourism (Dal, Naini Tal).
• Ecological: habitats for migratory birds and endemic life; India’s Ramsar sites now number over 90, many of them lakes.
• Scientific: lake sediments and varves archive past climates and earthquakes.

Recent Indian Issues

Glacial Lake Outburst Floods

• A glacial lake outburst flood (GLOF) is the sudden release of water from a moraine- or ice-dammed lake, triggered by ice or rock avalanches, landslides into the lake, heavy rain, seepage or piping through the moraine, or earthquakes.
• Warming is enlarging Himalayan glacial lakes, raising GLOF risk.
• Kedarnath (June 2013): the moraine-dammed Chorabari lake burst during extreme rain, compounding the Mandakini flood.
• South Lhonak, Sikkim (3–4 October 2023):
  • About 14.7 million m³ of frozen lateral moraine collapsed into the lake and raised a wave about 20 m high; roughly 50 million m³ of water breached the moraine dam.
  • The flood destroyed the 1,200 MW Teesta III dam at Chungthang, bridges and towns along the Teesta for about 385 km into West Bengal and Bangladesh; at least 55 people died and over 70 were missing.
• Response: the NDMA’s National GLOF Risk Mitigation Programme (2024) targets 189 high-risk lakes among roughly 7,500 Himalayan glacial lakes, with hazard assessment, automatic weather and water-level stations, early warning and lake-lowering.

Degradation and Conservation of Lakes

• Chilika: silting of its sea mouth degraded the lagoon, placing it on the Montreux Record (1993); a new mouth cut in 2000 restored salinity and fisheries, and it was removed in 2002, the first Asian wetland to be delisted.
• Loktak: thickening phumdis (floating biomass mats, carrying the Keibul Lamjao National Park) and the Ithai barrage have altered its hydrology; it remains on the Montreux Record.
• Sambhar: about 18,000 migratory birds died of avian botulism in November 2019; illegal brine extraction threatens the lake.
• Urban lakes: sewage, encroachment and weed growth shrink Dal, Wular and Bengaluru’s lakes; Bellandur has repeatedly frothed and caught fire.
• Policy: the Wetlands (Conservation and Management) Rules, 2017 and the National Plan for Conservation of Aquatic Ecosystems guide lake restoration.