The buoyant foundation
The defining feature of Loktak Lake is the phumdi, a heterogeneous mass of vegetation, soil, and organic matter in various stages of decomposition. These floating islands are found nowhere else on Earth. Their thickness varies from a few centimeters to over two meters, with approximately 80% of their mass submerged below the water's surface. This submerged portion provides buoyancy, allowing the entire mat to float. The core of a phumdi consists of black spongy detritus with a high content of organic carbon (36%) and nitrogen (2.08%).
The life cycle of a phumdi is tied to the seasonal fluctuation of the lake's water level. During the dry season, the water recedes, allowing the phumdi's roots to touch the lakebed and absorb nutrients. When the water level rises with the monsoon rains, the mats become buoyant again, floating to the surface. The construction of the Ithai Barrage in 1983 has kept the water level artificially high year-round. This prevents the phumdis from anchoring to the lakebed to absorb nutrients, causing them to thin and break apart.
Over 233 species of aquatic plants have been recorded in the lake's ecosystem. The vegetation on the phumdis is a mix of grasses and herbaceous plants, with dominant species including Zizania latifolia, Phragmites karka, and Leersia hexandra. These plants provide the structural integrity for the floating islands.
An ecosystem afloat
The largest and most consolidated phumdi is a 40-square-kilometer mass in the lake's southern region. This single floating island forms the Keibul Lamjao National Park, the only floating national park in the world. Established in 1977, the park is the last natural refuge for the endangered Sangai deer (Rucervus eldii eldii).
The Sangai, also known as the brow-antlered deer, has adapted specifically to this environment. Its hooves are suited for walking on the spongy surface of the phumdis. The deer's gait, a delicate trot as it navigates the unstable ground, has earned it the nickname "dancing deer". The park also supports other wildlife, including hog deer, otters, and wild boars, along with hundreds of bird species.
Human life is also integrated with the phumdis. An estimated 4,000 people live on the floating islands in small huts called "phumsangs". Fishermen build these shelters from bamboo, wood, and rock. They also create artificial, circular phumdis called "athaphums" which function as enclosures for fish farming, a practice that has existed for over 200 years.