Major Lakes of India

We have just finished tracing the paths of the mighty west-flowing peninsular rivers as they rush toward the Arabian Sea. Rivers are defined by their relentless motion. But what happens when water stops moving? When it finds a depression in the earth and simply pools, we get a lake.

Lakes are some of the most ecologically rich, economically vital, and visually stunning geographical features on the subcontinent. However, in geological terms, lakes are temporary. Over thousands of years, they naturally fill up with sediment brought in by rivers, or they dry up as climates change. Because they are temporary, the lakes we see today exist for very specific, active geographical reasons.

To truly understand India's lakes, we cannot just memorize a list of names and states. We have to understand how the earth made them. Once you know how a lake was formed, you will instantly know whether its water is fresh or salty, whether it is deep or shallow, and what kind of life it supports.

How Lakes are Formed: The Five Major Types

India's diverse geography—from the towering Himalayas to the long coastlines and arid deserts—means we have almost every type of lake on earth. We categorize them primarily by the geological forces that created their basins.

1. Tectonic Lakes (Created by Earth's Movements)

The earth's crust is not a single solid shell; it is made of massive puzzle pieces called tectonic plates that are constantly shifting. When these plates collide, pull apart, or grind against each other, the crust can fracture. Huge blocks of land can sink, creating deep depressions. When these depressions fill with rainwater or river water, a tectonic lake is born. Because these lakes are usually fed by mountain rivers and snowmelt, they are almost always freshwater lakes.

2. Crater Lakes (Created by Impacts or Volcanoes)

Sometimes, a lake basin is carved out from above. If a massive meteorite strikes the earth, it blasts a bowl-shaped crater into the rock. Alternatively, when a volcano erupts and eventually goes dormant, its collapsed top (the caldera) leaves a massive bowl. When rain fills these bowls, we get a crater lake.

Lonar Lake in the Buldhana district of Maharashtra is India's most famous crater lake. Around 50,000 years ago, during the Pleistocene Epoch, a meteorite weighing over a million tons slammed into the basaltic rock of the Deccan Plateau. Today, that impact crater is a lake. Because the water sits in a closed bowl of mineral-rich volcanic rock with no way to flow out, Lonar Lake is highly unique: its water is both saline (salty) and alkaline.

3. Coastal Lagoons (Created by the Ocean)

A lagoon is a shallow body of water separated from a larger body of water (like the ocean) by barrier islands, reefs, or sandbars. India has a massive coastline, and ocean waves are constantly moving sand along the shore. Over time, this sand can build up across the mouth of a bay, trapping the water inside.

Because lagoons are connected to the sea but also receive fresh water from inland rivers, their water is usually brackish—a mixture of fresh and salt water.

4. Fluvial Lakes (Created by Rivers)

Rivers, especially in their middle and lower courses on flat plains, tend to meander (bend and curve). Sometimes, a river loops so extremely that it eventually cuts straight across the narrow neck of the loop, abandoning the old curve entirely. The abandoned, U-shaped body of water is called an oxbow lake. Kanwar Lake in Bihar is Asia's largest freshwater oxbow lake, formed by the meandering of the Gandak river.

5. Aeolian Lakes (Created by Wind)

In arid and semi-arid regions like Rajasthan, the wind is a powerful sculptor. Strong winds can blow away loose desert sand, creating shallow depressions. During the brief monsoon, these depressions fill with water. Because the evaporation rate in the desert is incredibly high, the water quickly evaporates, leaving behind all the dissolved salts. These are usually inland saltwater lakes.

Deep Dive: Chilika Lake (The Coastal Lagoon)

If you travel to the coast of Odisha, you will find Chilika Lake, the largest coastal lagoon in India and the second largest in the world.

Geography and Formation

Chilika is pear-shaped, spread over the Puri, Khurda, and Ganjam districts of Odisha. It was formed by the action of the Bay of Bengal. Thousands of years ago, this area was just a wide bay. But the ocean waves, moving parallel to the coast, slowly dragged millions of tons of sand and deposited it across the bay's opening. This created a 60-kilometer-long sandbar that walled off the bay, turning it into a lagoon.

The Salinity Gradient (Why Chilika is Unique)

Chilika is famous for being a brackish water lagoon, but its saltiness is not uniform. In the northern part of the lake, major rivers like the Daya and Bhargavi empty their fresh water into the lagoon. (The Daya river is historically famous; its banks were the site of the ancient Kalinga War that transformed Emperor Ashoka). In the southern part, the lagoon has a narrow mouth that opens directly into the Bay of Bengal, allowing salty seawater to rush in with the tides.

This creates a fascinating "salinity gradient." The northern end is mostly fresh, the southern end is salty, and the middle is a perfect blend. Furthermore, during the monsoon, the rivers flood and push the seawater out, making the lake much fresher. In the dry winter, the river flow drops, and the seawater pushes deeper in, making the lake saltier.

Ecological Importance

Because of this dynamic environment, Chilika is an ecological goldmine.

• It is the largest wintering ground for migratory birds on the Indian subcontinent. Millions of birds fly here from as far away as Siberia and the Caspian Sea. The core area for these birds is the Nalabana Bird Sanctuary, an island in the lake that completely submerges during the monsoon.
• It is one of the only places in India where you can find the endangered Irrawaddy dolphin, known for its rounded forehead and lack of a prominent beak.

Deep Dive: Vembanad Lake (The Longest Lake)

Moving down to the southwestern coast of India, in the state of Kerala, we find Vembanad Lake. While Chilika is the largest by surface area, Vembanad holds the title for the longest lake in India, stretching for nearly 96.5 kilometers.

The Kayals of Kerala

In Kerala, coastal lagoons and backwaters are locally known as Kayals. Vembanad is the crown jewel of this backwater system. Like Chilika, it is separated from the Arabian Sea by a series of barrier islands. It spans several districts, and confusingly, it is known by different names depending on where you are standing. In the Kuttanad region, it is called Punnamada Lake; in Kochi, it is called Kochi Lake.

Rivers and Human Intervention

Vembanad is fed by several major rivers flowing down from the Western Ghats, most notably the Pamba and the Periyar.

Historically, Vembanad was a brackish lagoon, experiencing the same tidal push-and-pull of saltwater as Chilika. However, human intervention changed its geography. To protect the rice paddies of the Kuttanad region (which are actually situated below sea level) from saltwater intrusion during the dry season, the government built the Thanneermukkom Bund.

This massive saltwater barrier cuts the lake in half. It keeps the southern half permanently fresh (fed by rivers) and leaves the northern half brackish (connected to the sea). While this helped agriculture, it severely disrupted the natural flushing of the lake, leading to ecological issues like the explosive growth of water hyacinth (a weed that chokes the water).

Deep Dive: Sambhar Lake (The Inland Saltwater Lake)

When we think of salt water, we think of the ocean. So how does a lake sitting in the middle of the arid state of Rajasthan, hundreds of kilometers from the nearest sea, become the largest inland saltwater lake in India?

Welcome to Sambhar Salt Lake.

The Mechanics of an Endorheic Basin

To understand Sambhar, you must understand the concept of an endorheic basin.

Most lakes are part of an open drainage system. A river flows into the lake, and another river flows out of the lake, eventually carrying the water to the ocean. Because the water is constantly moving and flushing through, the lake stays fresh.

Sambhar Lake is an endorheic basin (a closed drainage basin). It is a massive, shallow bowl surrounded on all sides by the Aravalli hills. Four main seasonal rivers—the Mendha, Rupangarh, Khandel, and Khari—flow into this bowl. But no river flows out.

Why is it Salty?

As these rivers flow over the rocks and soils of Rajasthan, they dissolve tiny, invisible amounts of salt and minerals. They carry these minerals into Sambhar Lake. Because the lake has no outlet, the water just sits there. Under the blazing Rajasthan sun, the water evaporates rapidly. But evaporation only takes the pure H2O into the atmosphere; it leaves the heavy salt molecules behind.

Year after year, century after century, the rivers bring in a little bit of salt, and the sun evaporates the water, concentrating the salt. Today, Sambhar Lake is so salty that it is India's largest single source of inland salt production. During the dry season, the lake shrinks dramatically, leaving behind vast, blindingly white crusts of solid salt that are harvested by the state.

Deep Dive: Loktak Lake (The Floating Lake)

For our final major lake, we travel to the far northeast of India, to the state of Manipur. Here lies Loktak Lake, the largest freshwater lake in Northeast India. Loktak is unlike any other lake in the world because it appears to have solid land floating on top of it.

The Phumdis

Loktak Lake is famous for its phumdis. If you look at a photo of Loktak, you will see hundreds of green, circular islands dotting the water. These are not islands made of rock and dirt rising from the lake bed. They are floating mats of vegetation, soil, and organic matter at various stages of decomposition.

A phumdi forms when floating plant matter gets tangled together. Over years, dust and soil blow onto the mat, allowing larger plants to grow. The roots of these plants weave the mat tightly together. Only about 20% of a phumdi floats above the water; the remaining 80% is submerged, acting like a massive sponge.

Keibul Lamjao: The Floating National Park

The largest continuous phumdi in Loktak Lake covers an astonishing 40 square kilometers. It is so massive and thick that it was declared a national park—the Keibul Lamjao National Park. It is the only floating national park in the world.

This floating park is the last natural refuge of the Sangai, the brow-antlered deer of Manipur. The Sangai is often called the "dancing deer" because of its delicate, bouncing gait as it navigates the spongy, yielding surface of the phumdi.

The Ecological Crisis of the Ithai Barrage

To truly master this topic, you need to understand the modern threat to Loktak Lake. Historically, the phumdis had a fascinating lifecycle. During the monsoon, when the lake was full, the phumdis floated high. During the dry winter, the lake's water level would drop drastically. The phumdis would sink until they touched the lake bed. During this time, their roots would absorb essential nutrients from the soil at the bottom of the lake. When the rains returned, the nutrient-rich phumdis would float back up.

However, in the 1980s, the government built the Ithai Barrage (a dam) downstream to generate hydroelectric power. This barrage keeps the water level of Loktak Lake permanently high all year round.

Because the water level never drops, the phumdis never touch the lake bed anymore. Starved of nutrients, these incredible floating islands are slowly thinning, breaking apart, and dying, threatening the survival of the Sangai deer.

Worked Example: Analyzing Lake Characteristics

In competitive exams, you will often face "Assertion and Reason" questions or multi-statement analysis questions that test your deep understanding of lake mechanics, rather than just rote memorization. Let’s walk through how to solve one.

The Problem: Consider the following statements regarding Indian lakes:

1. 1Sambhar Lake's high salinity is primarily due to seawater intrusion from the Arabian Sea during high tides.
2. 2The construction of the Thanneermukkom Bund has permanently turned the entirety of Vembanad Lake into a freshwater body.
3. 3Loktak Lake is an example of a tectonic depression that is now characterized by floating vegetation.

Which of the statements given above is/are incorrect?

Step-by-Step Solution:

• Analyze Statement 1: We know Sambhar Lake is in Rajasthan. It is an inland lake and an endorheic basin. It is hundreds of kilometers away from the Arabian Sea. Its salinity comes from river-brought minerals and high evaporation, not seawater. Therefore, Statement 1 is incorrect.
• Analyze Statement 2: The Thanneermukkom Bund was built across Vembanad Lake to stop saltwater intrusion. However, it only protects the southern half (the Kuttanad agricultural region). The northern half, which connects to the sea at Kochi, remains brackish. It did not turn the entirety of the lake fresh. Therefore, Statement 2 is incorrect.
• Analyze Statement 3: Loktak Lake is located in the Manipur valley, which is a tectonic depression formed during the uplift of the Himalayas. It is indeed characterized by floating vegetation (phumdis). Therefore, Statement 3 is correct.

Conclusion: Since the question asks for the incorrect statements, the answer would be Statements 1 and 2.

By understanding the why behind the geography, you can easily dismantle trick questions that rely on half-truths.

Quick Revision

• Tectonic Lakes: Formed by fractures in the earth's crust. Usually freshwater. Example: Wular Lake (J&K).
• Crater Lakes: Formed by meteorite impacts or volcanic calderas. Example: Lonar Lake (Maharashtra), which is both saline and alkaline.
• Coastal Lagoons: Formed by sandbars blocking off a bay from the ocean. Usually brackish water. Examples: Chilika (Odisha), Vembanad (Kerala).
• Endorheic Basin: A closed drainage system where water flows in but cannot flow out, leading to high salinity through evaporation. Example: Sambhar Lake (Rajasthan).
• Chilika Lake: Largest coastal lagoon in India. Located in Odisha. Features a salinity gradient (fresh in north, salty in south). Home to Irrawaddy dolphins and Nalabana Bird Sanctuary.
• Vembanad Lake: Longest lake in India. Located in Kerala. Known as a 'Kayal' (backwater). Divided by the Thanneermukkom Bund. Hosts the Nehru Trophy snake boat race.
• Sambhar Lake: Largest inland saltwater lake in India. Located in Rajasthan. Fed by rivers like Mendha and Rupangarh. Major salt production site.
• Loktak Lake: Largest freshwater lake in Northeast India (Manipur). Famous for floating islands called phumdis. Home to Keibul Lamjao, the world's only floating national park, and the endangered Sangai deer.
• The Ithai Barrage: The dam that maintains high water levels in Loktak Lake, preventing phumdis from reaching the lake bed to absorb nutrients, thereby threatening their survival.