Bangladesh occupies 148,460 square kilometers in South Asia, positioned between 20°34' and 26°38' north latitude and 88°01' and 92°41' east longitude. The country shares 4,096 kilometers of land border with India wrapping around the north, east, and west, and 271 kilometers with Myanmar to the southeast. The Bay of Bengal forms the southern boundary with a coastline stretching 580 kilometers. This placement at the confluence of the Ganges, Brahmaputra, and Meghna river systems creates the world's largest delta, where approximately 700 rivers and tributaries drain a combined catchment area exceeding 1.72 million square kilometers. The deltaic plain covers roughly 80 percent of national territory, with elevations rarely exceeding 10 meters above sea level across most of the country. The remaining landmass divides between the Chittagong Hill Tracts in the southeast, reaching 1,064 meters at Mowdok Mual near the Myanmar border, the Madhupur Tract's Pleistocene terraces rising 6 to 12 meters above surrounding floodplains in central districts, and the Barind Tract's slightly elevated laterite plateau in the northwest Rajshahi Division.
The Ganges River enters Bangladesh from West Bengal at Shibganj in Chapainawabganj District, where it becomes known as the Padma River. This nomenclature shift occurs at the Indian border, though the same watercourse maintains both names in different contexts. The Padma flows southeast for approximately 356 kilometers through Bangladeshi territory, carrying an average annual discharge of 30,770 cubic meters per second measured at Hardinge Bridge. Peak flows during monsoon months from June through September can exceed 75,000 cubic meters per second. The Brahmaputra River crosses from India into Bangladesh at Kurigram District in the north, immediately adopting the local name Jamuna River. The Jamuna channel measures 6 to 14 kilometers wide during dry season and expands beyond 18 kilometers in monsoon periods, making it one of the world's widest rivers. Annual sediment load transported by the Jamuna alone reaches approximately 800 million tons. The Padma and Jamuna converge at Goalundo in Rajbari District, continuing jointly as the Padma until merging with the Upper Meghna River at Chandpur. From this triple confluence the combined Lower Meghna flows 160 kilometers south to the Bay of Bengal, discharging through multiple distributary channels with a combined width exceeding 13 kilometers at the estuary mouth.
Sediment deposition from these three river systems adds approximately 1 billion tons of alluvium annually to the delta, extending the coastline into the Bay of Bengal at varying rates. Satellite measurements between 1985 and 2015 documented net land gain of approximately 169 square kilometers despite concurrent erosion losses. This dynamic geomorphology creates char islands—temporary or semi-permanent land formations emerging from riverbed deposition. Current estimates identify over 1,000 char formations across Bangladesh, with total char land area fluctuating between 6,000 and 8,000 square kilometers depending on seasonal river levels. Individual chars range from ephemeral sandbars lasting single dry seasons to stable islands supporting permanent settlements. Hatiya Island in Noakhali District covers approximately 371 square kilometers but has shifted position and changed size repeatedly since first mapping in 1776. Bhola Island at the Meghna estuary mouth spans roughly 3,403 square kilometers, making it Bangladesh's largest island and among the world's largest river delta islands. The char formation process operates continuously—while new land accretes in some locations, riverbank erosion simultaneously displaces thousands of households annually, with government surveys estimating 8,000 to 10,000 hectares lost to erosion each year.
The Sundarbans mangrove forest extends across 10,000 square kilometers of coastal delta in Khulna, Satkhira, and Bagerhat districts, representing the Bangladeshi portion of a transboundary ecosystem spanning 140,000 hectares into India's West Bengal. This configuration makes it the world's largest contiguous mangrove forest. The name derives from sundari trees (Heritiera fomes), the dominant species historically, though top-dying disease has reduced sundari prevalence since the 1950s. Current forest composition shows gewa (Excoecaria agallocha) increasingly dominant in affected areas. The Sundarbans encompasses tidal waterways, mudflats, and small islands in a landscape where salinity varies from 12 to 30 parts per thousand depending on proximity to freshwater river inputs and seasonal monsoon dilution. Tidal range reaches 3 to 5 meters, inundating approximately 60 percent of forest area during daily high tides. The Bangladesh portion contains three wildlife sanctuaries established in 1977—Sundarbans South covering 36,970 hectares, Sundarbans East spanning 31,227 hectares, and Sundarbans West occupying 71,502 hectares. UNESCO designated the Sundarbans Reserved Forest a World Heritage Site in 1997, citing biodiversity values and ecological processes.
Royal Bengal tigers (Panthera tigris tigris) inhabit the Sundarbans at densities estimated between 106 and 274 individuals based on camera trap surveys conducted between 2015 and 2018. These population estimates vary significantly due to survey methodology differences and the challenges of monitoring wide-ranging animals in dense mangrove vegetation. The Sundarbans tiger population exhibits unique behavioral adaptations, swimming regularly between islands and demonstrating higher tolerance for saline water than mainland populations. Man-eating incidents occur with unfortunate regularity—forest department records document 50 to 60 human fatalities from tiger attacks annually through the 1990s and early 2000s, though recent figures show decline to approximately 20 to 30 deaths yearly following improved safety protocols for honey collectors and fishermen entering the forest. Estuarine crocodiles (Crocodylus porosus) maintain breeding populations in tidal creeks, with adults reaching 4 to 5 meters length. The forest supports approximately 260 bird species including masked finfoot (Heliopais personatus), brown-winged kingfisher (Pelargopsis amauroptera), and Goliath heron (Ardea goliath). Surveys have recorded 53 reptile species, 8 amphibian species, and approximately 400 fish species in associated waterways.
The Chittagong Hill Tracts comprise three districts—Rangamati, Khagrachhari, and Bandarban—covering 13,295 square kilometers in southeastern Bangladesh. This represents the country's only extensively hilly terrain, with elevation increasing gradually from east to west. The highest point, Mowdok Mual, stands at 1,064 meters according to Survey of Bangladesh measurements, though earlier sources cited Keokradong at 986 meters or Tazing Dong at 1,280 meters before GPS verification clarified elevations. The region receives Bangladesh's highest rainfall, with Rangamati District recording average annual precipitation exceeding 3,000 millimeters. This abundant moisture historically supported tropical and subtropical evergreen forests, though extensive logging and agricultural conversion have reduced forest cover from an estimated 90 percent in the 1960s to approximately 40 percent currently. The remaining forests contain species rare or absent elsewhere in Bangladesh, including Asian elephants (Elephas maximus), clouded leopards (Neofelis nebulosa), and hoolock gibbons (Hoolock hoolock). The western hoolock gibbon population in Bangladesh, concentrated in the Hill Tracts, numbers fewer than 300 individuals across fragmented forest patches according to primate surveys conducted between 2008 and 2012.
Kaptai Lake in Rangamati District formed following dam construction on the Karnaphuli River completed in 1962. The reservoir covers approximately 688 square kilometers at full capacity, making it Bangladesh's largest lake. Water level fluctuates seasonally between 32 meters and 39 meters above sea level as the hydroelectric facility manages flow. Lake creation inundated approximately 54,000 acres of cultivated land and displaced an estimated 100,000 people, predominantly from indigenous Chakma communities. Current fish production from the lake reaches approximately 9,000 to 11,000 metric tons annually, supporting commercial fisheries. The reservoir extends approximately 60 kilometers upstream from the dam, with highly irregular shoreline creating numerous coves and embayments. Several islands dot the lake surface, including decorated island resort developments.