Chilika is the largest brackish water lagoon of India with estuarine character that sprawls along the east coast. It is one of prime wintering ground for migratory water-fowl found anywhere on the Indian sub-continent. The total number of fish species are reported to be 180 and the fauna of lagoon was recorded over 800 species by the Zoological Surey of India which includes rare, threatened and endangered species including Barakudia limbless skink and Irrawady dolphin. The water spread of the lagoon varies between 1100 (monsoons) and 900 (summers) sq. kms. Dry months (December to June) drive in salt water from the Bay of Bengal through the 32 km long narrow channel that connects it from the sea and with the onset of rains (June to September) rivers falling into the northern zone push the sea water out. As a result of these dynamics the inlet mouth constantly changes position. The lagoon hosts over 211 species of birds in the peak migratory season. Birs from as far as the Caspian Sea, Lake Baikal, Aral Sea and other remote parts of Russia, Kirghiz steppes of Mongola, Central and Southeast Asia and from Himalayas come here. Nalabana island is a notified Sanctuary with an area of 15.5 sq km. The fauna at Chilika also includes species 18 mammals.

Sunderbans delta extends nearly 80,000 sq kms to the north of Bay of Bengal where three large rivers (Ganges, Brahmaputra and Meghna) meet the sea. The islands of the Sundarbans have been formed from silt deposits carried down from the Himalayas by rivers. They are said to be the largest estuarine forests in the world. The area has a vast network of creeks and channels with innumerable islands. This swampy region is the largest tract of mangroves in the world where seventy percent of the land gets flooded every day following the movement of the tides. Of the fifty true mangrove species in the world, Twenty six are found in the Sunderbans.

The biosphere reserve still preserves the natural habitat of over 200 Bengal tigers who have become strong swimmers moving from one island to another and have learnt to eat fish and crabs and also learnt to drink salt water. They are also known to attack fishermen and honey-collectors who venture in their territory. Tigers here are bigger and richer in colour than elsewhere in South Asia. Spotted deer, wild boar, monkeys, snakes, fishing cats, water monitors, Olive Ridley sea turtles and large estuarine crocodiles are the other wildlife to be seen.

The Nameri is one of the three National Parks of Assam with a core area of 200 sq kms and its adjoining forest reserves make a buffer zone of another 144 sq kms. The area is criss-crossed by the river Jia- Bhoroli and its tributaries namely the Diji, Dinai, Doigurung, Nameri, Dikorai, Kharietc. The Jia – Bhoroli river and the tributaries display devilish look when the incessant downpour in the upper reaches during the rainy season make it swell. The inaccessibility and continuity with neighbouring forest areas has helped the wildlife of Nameri to flourish. There is a good prey base in the form of Sambar, Barking deer, Hog Deer, Wild Boar and Gaurs for Tiger and Leopards. Nameri also qualify to be an Elephant Reserve with Elephant population estimated to be around 200.

On the banks of the Brahmaputra, Kaziranga National Park occupies 430 sq km, combining elephant grass with thorny rattan cane, areas of semi-evergreen forest and shallow swamps. The Karbi Anglong Hills rise South of the park, while the river forms its Northern boundary. There are a number of rivulets which flow down to the flood plain, bringing down rich silt and spreading out into shallow lakes. The habitat varies from marshes to grassland, woodland, rising to moist deciduous forests and finally to tropical semi-evergreen forests.

Kaziranga was declared a game reserve to save the Indian one-horned rhino which had become threatened with extinction at the turn of the twentieth century. The present rhino population is over 1,800 which could be easily spotted in the marshes and grasslands.

Kaziranga contains significant populations of 34 other mammal species including large herbivores like elephants, gaurs and sambar. Small herbivores include the Indian Muntjac, wild boar, and hog deer. Kaziranga is one of the few wild breeding areas outside Africa for multiple species of large cats, such as Royal Bengal Tigers and Leopards. Other felids include the Jungle Cat, Fishing Cat, and Leopard Cats. Small mammals include the rare Hispid Hare, Indian Gray Mongoose, Small Indian Mongooses, Large Indian Civet, Small Indian Civets, Bengal Fox, Golden Jackal, Sloth Bear, Chinese Pangolin, Indian Pangolins, Hog Badger, Chinese Ferret Badgers, and Particolored flying squirrels. Nine of the 14 primate species found in India, prominent out of which are the Assamese Macaque, Capped, Golden Langur, as well as the only ape found in India, the Hoolock Gibbon. Kaziranga’s rivers are also home to the endangered Ganges Dolphin.

Kaziranga has been identified by Birdlife International as an Important Bird Area. It is home to a variety of migratory birds, water birds, predators, scavengers, and game birds. Birds such as the Lesser White-fronted Goose, Ferruginous Duck, Baer’s Pochard duck and Lesser Adjutant, Greater Adjutant, Black-necked Stork, and Asian Openbill stork migrate from Central Asia to the park during winter. Riverine birds include the Blyth’s Kingfisher, White-bellied Heron, Dalmatian Pelican, Spot-billed Pelican, Spotted Greenshank, and Black-bellied Tern. Birds of prey include the rare Eastern Imperial, Greater Spotted, White-tailed, Pallas’s Fish Eagle, Grey-headed Fish Eagle, and the Lesser Kestrel. Other families of birds inhabiting Kaziranga include the Great Indian Hornbill and Wreathed Hornbill, Old World babblers such as Jerdon’s and Marsh Babblers, weaver birds such as the common Baya Weaver, threatened Finn’s Weavers, thrushes such as Hodgson’s Bushchat and Old World warblers such as the Bristled Grassbird. Other threatened species include the Black-breasted Parrotbill and the Rufous-vented Prinia.

Two of the largest snakes in the world, the Reticulated Python and Rock Python, as well as the longest venomous snake in the world, the King Cobra, inhabit the park. Other snakes found here include the Indian Cobra, Monocled Cobra, Russell’s Viper, and the Common Krait.