Every city has a feature it returns to, and in Chittagong that feature is water. The Karnaphuli River runs past the port, under bridges, beside markets and industrial estates, and out to the Bay of Bengal. It is not a backdrop. It is the route by which much of Bangladesh's trade arrives and leaves, the source of power from a dam far upstream, the waterway that once connected hill communities to the coast, and the river that a growing city now puts under strain. To follow the Karnaphuli is to follow the region's history in a single, moving line.
The river begins far from the sea. It rises at Saithah village in Mamit district in Mizoram, India, in the Lushai Hills, and flows about 270 kilometres south-west through the Chittagong Hill Tracts and Chittagong district before reaching the Bay of Bengal at the Patenga–Anwara coast. In Mizo it is known as Khawthlangtuipui, meaning western river; in Chakma it is called Borgang, meaning big river. Its principal tributaries include the Kawrpui or Thega River, the Tuichawng River and the Phairuang River. The river is described as the largest and most important river in Chittagong and the Chittagong Hill Tracts, and as representing the drainage system of the whole south-western part of Mizoram. Those descriptions are geographical, but they also hint at something cultural: this is a river that belongs to more than one landscape, language and livelihood.
A name from a legend
The name Karnaphuli itself carries a story that is told as legend rather than history. The Daily Star, retelling material from Thomas Herbert Lewin's book A Fly on the Wheel, recounts an old name for the river, Kaincha Khal, and a moonlit boat ride taken by a prince and a princess. A flower tucked in the princess's hair fell into the water; she jumped in to retrieve it and was carried away by the current; the prince dived after her and also drowned. The name is said to come from karnaphul, the flower adorning the ear. Another version of the legend, widely repeated, says the princess lost an earring in the water. The details vary, as legends do, but the point of the story does not: the river has long been imagined as beautiful, fast and unforgiving, a place where a moment's loss becomes permanent.
That swiftness is part of the river's physical character. The Karnaphuli is described as the fastest flowing river in Bangladesh after the Padma, and at one measured point it is 667 metres wide. For people who lived along it before modern roads, that current was both a highway and a hazard. Boats carried people and commercial goods when road and bridge links were poor, and the river was, in the Daily Star's phrase, what holds the port city — the life of Chattogram. Even today, when a traveller crosses by bridge or tunnel, the boats below — cargo vessels, ferries, fishing boats and small commuter craft — are a reminder that the river is still worked every day.
The port at the mouth
At the river's mouth stands the reason the Karnaphuli matters far beyond Chittagong. The Port of Chattogram, at the mouth of the river, is the largest and busiest seaport in Bangladesh. Ships anchor in the river, cargo moves between ship and shore, and the city's economy turns on that movement: imports arriving for factories and markets across the country, and exports leaving for buyers overseas. The port is not separate from the river; it is the river made into infrastructure, with jetties, a dry dock, a refinery and a naval presence clustered near its banks, and with the city itself largely on its northern bank.
The river's role as a connector did not end with the port. A railway bridge at Kalurghat was built in 1931 and later converted into a rail and road bridge in 1962, connecting the city with southern upazilas and districts including Bandarban and Cox's Bazar. Two further bridges followed in the Chaktai area, in 1990 and 2010, according to the Daily Star. Then, in October 2023, the pattern changed again: instead of crossing over the river, traffic began to pass beneath it. The Bangabandhu Sheikh Mujibur Rahman Tunnel, opened on 28 October 2023, runs 3.32 kilometres under the Karnaphuli, connecting the port city on the north bank with Anwara upazila on the south. It was described at its opening as Bangladesh's first tunnel and the first under-river road tunnel in South Asia, built on a one city, two towns model and intended to shorten the route towards Cox's Bazar. Whether one crosses by the old Kalurghat bridge, the Shah Amanat Bridge or the tunnel, the crossing is part of the experience of Chittagong: the city is divided by water and joined by engineering.
Power from the hills
Upstream, the Karnaphuli does a different kind of work. At Kaptai, in Rangamati district, the Kaptai Dam impounds the river to form Kaptai Lake, the reservoir for the Karnafuli Hydroelectric Power Station. The station was constructed in 1962 and is the only hydroelectric power plant in Bangladesh, with a total output of 230 megawatts. That single fact gives the river a national role that is easy to overlook from the port: the same water that carries container ships at its mouth also turns turbines in the hills.
Kaptai Lake itself has become a landscape in its own right — Bangladesh's largest man-made lake, known for its scenery, fisheries and tourism — but the dam also changed the river. Research and reference writing on the Karnaphuli notes that the dam altered the natural flow, reduced sediment downstream, disrupted fish migration and changed water quality, while the reservoir brought its own pressures, including sedimentation and pollution in parts of the lake. The trade-off is familiar across the world's dammed rivers: electricity and a reservoir on one side, a changed ecology on the other. The Karnaphuli makes that trade-off visible within a single river system, from a hill reservoir to a tidal port.
Fishing, farming and daily life
Between the dam and the sea, the river supports a quieter economy. Fishing communities work its waters and its estuary, and the river's fish have long included carp such as rui, katla and mrigal, catfish such as magur and shing, and shrimp and prawns, with species varying by location and salinity. The river is also home to the endangered Ganges river dolphin. Hilsa, once common in the river, have nearly disappeared from it, a change attributed in reference writing to pollution. Those two facts sit side by side and say a great deal: the river still holds remarkable wildlife, and it has already lost some of what it once held.
For the hill tracts, the river has also been a route and a boundary, a way to move timber, produce and people towards the coast, and a link between communities that otherwise live in steep, forested terrain. For Chittagong city, it has been a source of water, a place for evening walks and boat rides, and a working waterfront where sailors' clubs, bridges and river roads give views of ships at anchor. A visitor who takes a boat on the Karnaphuli, or simply watches the river from the Shah Amanat Bridge at dusk, sees the region's working life without a filter: cranes and hulls on one side, fishing boats and ferry passengers on the other, and the hills fading behind the city.
A river under pressure
That working life is also the source of the river's most serious problems. The Karnaphuli is heavily polluted, by industrial effluent discharged directly into the river, by untreated domestic and medical waste from the city, and by agricultural runoff carrying pesticides and fertilisers. Factories and industrial sites along its banks — including fertiliser, paper and rayon, refinery and dry-dock operations named in water-quality studies — have historically used the river both for transport and for waste disposal. The result, in the language of those studies, is a deterioration of water quality, with organic pollutants, heavy metals and pathogens, and with reduced oxygen available for aquatic life. Deforestation in the hill tracts adds sediment, which can smother habitats, clog waterways and reduce the effectiveness of flood control.
None of this is unique to the Karnaphuli, and none of it is abstract for the people who live beside it. Pollution affects fishing livelihoods, the safety of water for drinking and other uses, and the health of the ecosystem on which the river's dolphins, fish and riverside communities depend. Efforts described in general writing on the river include pollution control, better waste management and more sustainable land use, but the same writing stresses that more comprehensive and coordinated action is needed. The river's future, in other words, will be decided less by any single project than by whether the city and industries that depend on it treat it as infrastructure to be maintained rather than as a convenient outlet.
The Karnaphuli rewards a slower way of looking. It is easy, from a bridge, to see only traffic. It is harder, and more rewarding, to hold the whole river in mind at once: a hill stream in Mizoram, a reservoir and power station at Kaptai, a working port at its mouth, a tunnel beneath its bed, and a city that grew up because the water was there. The river feeds the port, the city and the hills behind it not in the sense of a single gift, but as a continuous exchange — water for power, passage for trade, fish for tables, and a route home for people crossing from one bank to the other. If Chittagong keeps that exchange in balance, the Karnaphuli will remain what its name, in legend and in daily use, has always suggested: not just a river running through a region, but the river that holds the region together.