Some people in Manipur live in houses built on floating islands of weeds and decaying vegetation held together by suspended silt. These islands are called

1. Classification of Indian Lakes (basic)

To understand Indian lakes, we must look at how they are formed, as their origin determines their chemistry, size, and ecological importance. India’s diverse landscape—from the towering Himalayas to the arid deserts of Rajasthan and the long coastlines—creates a variety of lake types. Broadly, we classify them based on their formation processes: Tectonic, Glacial, Fluvial (river-related), Aeolian (wind-related), and Coastal.

Most of the freshwater lakes in the Himalayan region are of Glacial origin, formed when glaciers scooped out basins that were later filled by snowmelt, such as Nainital and Bhimtal CONTEMPORARY INDIA-I, Drainage, p.22. In contrast, Wular Lake in Jammu and Kashmir, India's largest freshwater lake, is primarily the result of tectonic activity—fractures in the Earth's crust that created a natural depression Geography of India, The Drainage System of India, p.32. Other tectonic lakes include the high-altitude Pangong Tso and Tso Moriri in Ladakh Geography of India, The Drainage System of India, p.28.

Outside the mountains, we find lakes formed by different forces. In arid regions like Rajasthan, Aeolian (wind) action creates saltwater lakes such as Sambhar Lake, which is vital for salt production CONTEMPORARY INDIA-I, Drainage, p.22. Along the coast, the interaction of the sea and rivers creates Lagoons or Brackish water lakes. For instance, Chilika Lake in Odisha, the largest coastal lake in India, was formed by the silting action of the Mahanadi River trapping seawater behind a barrier Geography of India, The Drainage System of India, p.29. Finally, there are unique cases like Loktak Lake in Manipur, famous for its Phumdis—floating islands of heterogeneous vegetation and organic matter that support entire local communities Geography of India, The Drainage System of India, p.30.

Type of Lake	Primary Formation Agent	Key Examples
Tectonic	Crustal movements/faults	Wular Lake (J&K), Pangong Tso (Ladakh)
Glacial	Ice scouring and snowmelt	Nainital, Bhimtal (Uttarakhand)
Aeolian	Wind erosion in arid basins	Sambhar Lake (Rajasthan)
Coastal/Lagoon	Oceanic deposits and river silting	Chilika Lake (Odisha), Pulicat Lake
Volcanic	Crater/Caldera collapse	Lonar Lake (Maharashtra)

Sources: CONTEMPORARY INDIA-I, Drainage, p.22; Geography of India, The Drainage System of India, p.28; Geography of India, The Drainage System of India, p.29; Geography of India, The Drainage System of India, p.30; Geography of India, The Drainage System of India, p.32; Physical Geography by PMF IAS, Volcanism, p.151

2. Ramsar Convention and Indian Wetlands (intermediate)

To understand Indian wetlands, we must first look at the Ramsar Convention, an intergovernmental treaty adopted in 1971 in Ramsar, Iran. It represents a global commitment to the 'wise use' of wetlands—meaning the maintenance of their ecological character through ecosystem-based approaches. India became a contracting party to this convention in 1982 Environment, Shankar IAS Academy (ed 10th), International Organisation and Conventions, p.398. Wetlands are often called the 'Kidneys of the Landscape' because they filter pollutants, recharge groundwater, and provide a vital habitat for diverse flora and fauna.

A crucial sub-category within the Ramsar framework is the Montreux Record. Think of this as a 'Red Alert' register for sites where the ecological character has changed, or is likely to change, due to human interference or pollution. Currently, two Indian sites are on this list: Keoladeo National Park (Rajasthan) and Loktak Lake (Manipur) Environment, Shankar IAS Academy (ed 10th), International Organisation and Conventions, p.397. A success story worth noting is Chilika Lake in Odisha, which was placed on the Montreux Record in 1993 but removed in 2005 after successful restoration efforts.

Among India's designated sites, Loktak Lake is particularly unique. It is the largest freshwater lake in Northeast India and is famous for its Phumdis—heterogeneous masses of vegetation, soil, and organic matter that form floating 'islands' Geography of India, Majid Husain (9th ed.), The Drainage System of India, p.30. These mats are thick enough to support human huts and the world's only floating national park, Keibul Lamjao. India's wetlands vary immensely in scale, from the massive Vembanad Kol in Kerala (over 1,500 km²) to the tiny, high-altitude Renuka Lake in Himachal Pradesh Geography of India, Majid Husain (9th ed.), Natural Vegetation and National Parks, p.54.

Sources: Environment, Shankar IAS Academy (ed 10th), International Organisation and Conventions, p.397-398; Geography of India, Majid Husain (9th ed.), The Drainage System of India, p.30; Geography of India, Majid Husain (9th ed.), Natural Vegetation and National Parks, p.53-54

3. Drainage and Physiography of North-East India (intermediate)

The North-East of India, often referred to as the 'Seven Sister States,' possesses a unique physiographic identity known as the Purvanchal. These are the eastern extensions of the Himalayas, running along India's border with Myanmar. Unlike the high, snow-clad peaks of the Great Himalayas, the Purvanchal consists of medium-height hills heavily draped in lush forests. As you move from north to south, these ranges take on local names: the Patkai-Bum in Arunachal Pradesh, the Naga Hills, the Manipur Hills, and the Mizo Hills (also called the Blue Mountains) Geography of India, Physiography, p.17. A crucial link in this chain is the Barail Range, which connects the Purvanchal to the Meghalaya Plateau in the west.
The drainage system here is equally distinct, dominated by the Brahmaputra and the Barak River. The Barak rises from Mt. Japvo in Nagaland and follows a dramatic path, making a sharp hair-pin bend in Manipur before flowing through the Cachar district of Assam. This basin is home to Mawsynram and Cherrapunji, regions that receive the highest rainfall globally, causing the Barak to carry a massive volume of water. Eventually, the Barak enters Bangladesh, where it is known as the Surma, later joining the Padma to become the mighty Meghna before entering the Bay of Bengal Geography of India, The Drainage System of India, p.18.
Nested within this complex geography is Loktak Lake in Manipur, the largest freshwater lake in Northeast India. What makes Loktak globally unique are the Phumdis. These are not just floating plants; they are heterogeneous, thickened mats of vegetation, soil, and organic matter in various stages of decay. These floating 'islands' are sturdy enough to support phumsang (huts) built by local fishermen, creating a rare ecosystem where human life and biodiversity literally float on water Geography of India, The Drainage System of India, p.30.

Feature	Description
Barak River	Originates at Mt. Japvo; becomes the Meghna in Bangladesh.
Phumdis	Floating islands of organic matter unique to Loktak Lake.
Purvanchal	Tertiary mountain range running along the Indo-Myanmar border.

Sources: Geography of India, Majid Husain, Physiography, p.17; Geography of India, Majid Husain, The Drainage System of India, p.18; Geography of India, Majid Husain, The Drainage System of India, p.30

4. Biodiversity Hotspots and Endemic Species of NE India (exam-level)

To understand the ecological importance of North-East (NE) India, we must first master the concept of a Biodiversity Hotspot. This term isn't just a label for a beautiful place; it refers to regions that are both biologically rich and under significant threat. To qualify, a region must harbor at least 1,500 species of vascular plants as endemics and must have lost at least 70% of its original habitat. India is home to four such global hotspots: The Himalayas, The Indo-Burma region, The Western Ghats & Sri Lanka, and Sundaland (which includes the Nicobar Islands) Environment, Shankar IAS Academy, Protected Area Network, p.222.

NE India is unique because it acts as a "transition zone" where two of these hotspots meet. While the Himalayan hotspot covers the high-altitude regions, the Indo-Burma hotspot is particularly expansive. It stretches from Eastern Bangladesh through Myanmar and Southeast Asia, but crucially, within India, it includes the land south of the Brahmaputra River, encompassing states like Manipur, Mizoram, and Nagaland Environment, Shankar IAS Academy, Protected Area Network, p.223. This geographical placement explains why the region serves as a gateway for species migrating between the Indian subcontinent and Southeast Asia.

A central pillar of these hotspots is Endemism—the phenomenon where a species is found in one specific geographic location and nowhere else on Earth. Endemism is a sign of high evolutionary specialization. In India, about 18% of plants are endemic, and among amphibians, a staggering 62% are unique to the country Environment and Ecology, Majid Hussain, BIODIVERSITY, p.23. In the context of NE India's wetlands, like Loktak Lake, this endemism is perfectly illustrated by the Sangai (the Brow-antlered deer). This deer is endemic specifically to the Phumdis (floating mats of vegetation) of Keibul Lamjao National Park; if this specific habitat is lost, the species vanishes from the wild forever.

Hotspot	NE India Coverage	Key Characteristics
Himalayas	Arunachal Pradesh, Sikkim	High altitude, alpine flora, home to the Red Panda.
Indo-Burma	Manipur, Mizoram, Nagaland, etc. (South of Brahmaputra)	Tropical forests, high avian diversity, unique wetland endemism.

Sources: Environment, Shankar IAS Academy, Protected Area Network, p.222-223; Environment and Ecology, Majid Hussain, BIODIVERSITY, p.23

5. Keibul Lamjao: The World's Only Floating National Park (exam-level)

Imagine a national park where the ground beneath your feet isn't solid earth, but a floating carpet of vegetation. This is Keibul Lamjao National Park in Manipur, the only floating protected area in the world. Located in the southeastern part of Loktak Lake—the largest freshwater lake in Northeast India—this park is a marvel of nature's engineering. The "soil" here consists of Phumdis: heterogeneous masses of matted vegetation, decaying organic matter, and soil held together by roots and trapped silt Geography of India, Majid Husain, p.30. These floating islands are buoyant enough to support not just rich wildlife, but also human huts and local fishing communities.

The ecological significance of this park cannot be overstated. It was designated a Ramsar site in 1990 due to its international importance as a wetland Geography of India, Majid Husain, p.30. Beyond its unique geography, it serves as the last natural refuge for the critically endangered Sangai (Brow-antlered deer), often called the "dancing deer" because of its delicate gait while balancing on the spongy phumdis. This habitat is a delicate balance of nature where the lake's water levels, the thickness of the phumdis, and the nutrient cycle must remain in harmony to sustain the life atop it Science, Class VIII NCERT, p.204.

Feature	Description
Primary Habitat	Floating Phumdis (matted organic matter and soil).
Flagship Species	Sangai (Brow-antlered deer).
Hydrological Role	Source for hydro-power, irrigation, and local livelihood Geography of India, Majid Husain, p.30.

Sources: Geography of India, Majid Husain, The Drainage System of India, p.30; Science, Class VIII NCERT, How Nature Works in Harmony, p.204; Contemporary India-I, Geography Class IX NCERT, Natural Vegetation and Wildlife, p.43

6. Loktak Lake and the Phumdi Ecosystem (exam-level)

Located in the state of Manipur, Loktak Lake is the largest freshwater lake in Northeast India and is globally famous for its unique Phumdi (or Phundi) ecosystem. Phumdis are heterogeneous masses of vegetation, soil, and organic matter in various stages of decomposition that float on the lake's surface like islands. These floating mats are strong enough to support the weight of human settlements, and local fishermen actually build huts atop them to live and work. Due to its immense ecological and socio-economic importance, it was designated as a Ramsar site in 1990 Geography of India, The Drainage System of India, p.30.

The southern part of the lake hosts the Keibul Lamjao National Park, which is the only floating national park in the world. This park is the sole natural habitat of the critically endangered Sangai deer (the state animal of Manipur), also known as the 'dancing deer' because of its rhythmic walk on the spongy phumdis. The phumdis follow a natural cycle: during the dry season, they sink to the lake bed and pick up essential nutrients from the soil; when the water levels rise during the monsoon, they float back up. This nutrient exchange is vital for the vegetation to thrive and support the herbivorous Sangai Geography of India, The Drainage System of India, p.30.

Despite its beauty, the lake faces ecological threats. The construction of the Ithai Barrage for hydropower generation has maintained high water levels year-round, preventing the phumdis from sinking and 'recharging' their nutrients. This has caused the mats to thin out, threatening the survival of the Sangai. Consequently, Loktak Lake is listed under the Montreux Record, a register of Ramsar sites where changes in ecological character have occurred or are likely to occur.

Feature	Description
State	Manipur (Bishnupur district)
Key Species	Sangai (Brow-antlered deer)
Conservation Status	Ramsar Site & Montreux Record
Unique Formation	Phumdis (Floating biomass islands)

Sources: Geography of India, The Drainage System of India, p.30

7. Solving the Original PYQ (exam-level)

This question bridges your knowledge of Regional Geography and Ecological Ecosystems. Having recently studied the Drainage System of India, you should recognize Loktak Lake as a vital freshwater body in Northeast India. The building blocks of this concept involve understanding how biogeochemical processes allow matted vegetation and soil to stabilize into floating landmasses. As a coach, I want you to see this not just as a naming exercise, but as a classic example of human adaptation to a unique wetland environment, specifically within the Indo-Burma biodiversity hotspot.

To arrive at the correct answer, Phoomdis (or Phumdis), focus on the specific geographical marker: Manipur. When you see 'floating islands' and 'Manipur' in the same sentence, your mind should immediately link to the Keibul Lamjao National Park, which is the world's only floating national park and the natural habitat of the endangered Sangai deer. The reasoning follows a clear path: identify the unique ecosystem (freshwater lake), recall the local nomenclature for its floating biomass, and confirm its utility for human settlements. This specific terminology is well-documented in Geography of India by Majid Husain.

UPSC often uses distractors from entirely different geographical or cultural contexts to test your precision. For example, Tipis are conical tents used by indigenous North Americans, and an Izba is a traditional Russian timber house; both are cultural architectural terms rather than ecological features. Meanwhile, Barkhans are crescent-shaped sand dunes formed by aeolian processes in deserts. By recognizing that these three options belong to Arid or Cultural Geography, you can eliminate them and confidently select the only term that fits a lentic (still water) ecosystem.