The Bay of Bengal is known for being one of the largest bays in the world, a major cyclone hotspot, a critical hub for international trade, and a region of extraordinary biodiversity. Covering roughly 839,000 square miles of the northeastern Indian Ocean, it borders India and Sri Lanka to the west, Bangladesh to the north, and Myanmar and the Malay Peninsula to the east. Its combination of warm waters, massive river systems, and strategic location has shaped the economies, ecosystems, and weather patterns of South and Southeast Asia for centuries.
Sheer Size and Depth
The Bay of Bengal is the largest bay in the world by surface area, stretching between roughly 5° and 22° North latitude. Despite its vast footprint, it’s considered relatively shallow for an oceanic body of its size, though its deepest point drops to about 15,400 feet (4,694 meters). The southern boundary runs from the tip of Sri Lanka in the west to the northern end of Sumatra in the east, making it a distinct basin within the broader Indian Ocean.
A Global Cyclone Hotspot
The bay is one of the most cyclone-prone bodies of water on Earth. Several factors converge to make it ideal for tropical storm formation: consistently warm sea surface temperatures, high humidity in the lower and middle atmosphere, strong low-level spin from tropical disturbances, and relatively low wind shear between the upper and lower atmosphere. The surrounding monsoon trough feeds moisture and instability into the system, creating conditions that spawn powerful cyclones year after year.
These storms frequently strike the low-lying coastlines of Bangladesh, India, and Myanmar, where they cause devastating flooding and storm surges. Bangladesh, in particular, sits at the northern head of the bay where the funnel-shaped coastline amplifies incoming surges. Some of the deadliest natural disasters in recorded history have been Bay of Bengal cyclones.
Rivers That Reshape the Sea
Three of Asia’s great rivers converge before emptying into the bay: the Ganges, the Brahmaputra, and the Meghna. Together, the Ganges-Brahmaputra-Meghna system forms one of the largest river basins on the planet, delivering an enormous volume of freshwater and sediment. The Brahmaputra alone averages about 20,000 cubic meters of water per second at its key monitoring station, and the combined flow at the Padma (where the Ganges and Brahmaputra merge) reaches roughly 30,000 cubic meters per second.
All that freshwater creates a distinctive low-salinity layer across the bay’s surface, which influences ocean circulation, nutrient distribution, and marine life. The sediment carried by these rivers built the Ganges-Brahmaputra Delta, the largest river delta in the world, and continues to reshape the northern coastline.
The Sundarbans Mangrove Forest
Where those rivers meet the bay sits the Sundarbans, the largest contiguous mangrove forest on Earth and a UNESCO World Heritage Site since 1987. It is the only mangrove habitat in the world that supports a population of wild Bengal tigers, earning it the nickname “the only tiger mangrove land on Earth.”
The Sundarbans faces serious pressure. Satellite analysis shows mangrove coverage in parts of the forest shrank from about 73 square kilometers in the late 1980s to roughly 58 square kilometers by 2006, driven by a combination of tectonic shifts, rising sea levels, and human encroachment. Several species that once thrived there are now extinct or critically threatened.
Rich but Threatened Marine Life
The bay supports a wide range of marine megafauna, from dolphins and whales to sharks, rays, and sea turtles. Surveys in the northern Bay of Bengal have recorded over 160,000 individual sharks and rays across 88 species, spanning 30 shark and 58 ray species. Five globally threatened species of marine turtle inhabit these waters, including the well-known Olive Ridley sea turtle, which nests along the bay’s western shores in enormous groups called arribadas.
Sharks and rays in the bay are heavily harvested for liver oil (valued for its vitamin content), fins used in soup, and to a lesser extent for meat and hides. Conservation frameworks remain patchy. Bangladesh, despite being home to all five threatened turtle species, has not yet signed the international agreement on marine turtle conservation in the Indian Ocean.
An Oxygen-Depleted Middle Layer
Beneath the bay’s productive surface waters lies one of the world’s recognized oxygen minimum zones, a band of water where dissolved oxygen drops to near zero. In the Bay of Bengal, this low-oxygen layer typically sits between about 50 and 800 meters deep. It intensifies seasonally: after the monsoon, river discharge from systems like the Godavari fuels a bloom of organic matter that consumes oxygen as it decomposes. During the fall months, oxygen levels near the river mouth can plunge to virtually zero at depths as shallow as 35 to 45 meters, compared to healthier levels of 1 to 1.5 milliliters per liter during summer.
Compared to similar zones in the Arabian Sea and eastern tropical Pacific, the Bay of Bengal’s oxygen minimum zone is considered weaker overall. But its seasonal pulses can still disrupt food webs and coastal fisheries by altering the habitat available to fish and other marine organisms.
Centuries as a Trade Crossroads
The Bay of Bengal has been a major maritime trade corridor for well over a thousand years. Ancient and medieval trade routes connected the Indian subcontinent with Southeast Asia, China, and beyond, carrying spices, textiles, and other goods across its waters. By the 19th century, the bay became the backbone of colonial commerce: Bengali jute, Ceylonese coffee, Burmese rice, Malayan rubber, and Javanese sugar all moved along its shipping lanes.
Calcutta (now Kolkata) rose to become the most important hub of British trade and administration in Asia, connecting routes from the Malacca Strait in the east to Africa and the Mediterranean in the west. The British established strategic footholds around the bay’s rim, taking Penang in 1786, Colombo in 1796, and Singapore in 1819, all to protect and expand their trading networks. When the Suez Canal opened in 1869, it slashed shipping times and costs, further boosting trade volumes through the bay. By 1871, nearly all textile exports to Bombay and about 20 percent of bulk exports from Calcutta passed through the canal.
Today, the bay remains a vital corridor for energy shipments and container traffic between the Middle East, South Asia, and East Asia.
Natural Resources Beneath the Seabed
The bay’s floor holds significant reserves of oil and natural gas. India’s hydrocarbon resource assessment estimates about 371 million metric tons of oil equivalent in the Andaman Basin alone, one section of the bay’s eastern waters. Bangladesh and Myanmar also have substantial offshore gas fields, making the bay an increasingly contested space for energy exploration and geopolitical competition.
The World’s Longest Natural Beach
Cox’s Bazar, on the southeastern coast of Bangladesh, runs 120 kilometers (75 miles) along the bay, making it the longest unbroken natural sea beach in the world. At high tide, the beach averages about 200 meters wide; at low tide, it expands to roughly 400 meters. It draws millions of domestic tourists each year and has become a symbol of Bangladesh’s coastal identity.