Karnafuli River the largest and most important river in chittagong and the chittagong hill tracts, originating in the Lushai hills in Mizoram State of India. It travels through 180 km of mountainous wilderness making a narrow loop at rangamati and then follows a zigzag course before it forms two other prominent loops, the Dhuliachhari and the kaptai. The Rangamati and the Dhuliachhari loops are now under the reservoir of the Kaptai earth-filled dam. The hydroelectric dam is situated just before the entrance of the river into the Kaptai loop. After coming out from the Kaptai loop the river follows another stretch of tortuous course through the Sitapahar hill range and flows across the plain of Chittagong after emerging from the hills near Chandraghona. Therefore, the river drains into the bay of bengal cutting across several hill ranges, viz the Barkal, Gobamura, Chilardak, Sitapahar and Patiya of the Chittagong Hill Tracts and Chittagong. It has possibly maintained its older course keeping pace with the uplift of the hill ranges and can be classified as an antecedent river. The Karnafuli is narrow and straight from Prankiang to waggachhari along Kaptai-Chandraghona road. The straightness of the river is probably due to a fault, which controlled the channel from Prankiang to Wagga. The main tributaries of the Karnafuli are the kasalong, Chengi, halda and Dhurung on the right and the Subalong, Kaptai, Rinkeong and Thega on the left.
Flowing to the west through rangunia upazila and then keeping raozan upazila on the north and boalkhali upazila on the south, it receives the waters of the Halda river at Kalurghat just above the railway bridge. It then turns south, receives the waters of the Boalkhali and other khals and turns west circling round the eastern and southern sides of Chittagong Town. From the extreme corner of the chittagong port to the west, it moves southwest to fall into the Bay of Bengal 16.89 km below. It is navigable throughout the year by sea-going vessels up to Chittagong Port and by large boats, shallow draughts and all sorts of freighters and launches up to Kaptai river in the Hill Tracts.
In Chittagong the Karnafuli made a most significant change in its course from Kalurghat downwards. The change has been taking place for more than a century. Formerly, the river had a western and southwestern course from Kalurghat and flowed by Sampanghata, Suloop Bahar, Kapashgola, Chowk Bazar, Roomghata, Ghat Farhadbeg, Boxirhat, Patharghata on its rightbank. But gradually it receded to the left throwing up vast and extensive alluvial lands along its rightbank, now known as Char Bakalia, Chandgaon, Char Chaktai, etc. The above ghats and bazars which once dotted the right bank of the Karnafuli along the eastern limits of the town are now important localities in and outside the municipality, far away from the present course of the river. This fact is of much historical importance in so far as it helps locate the eastern bounds of the town during the Mughal and early British period.
There is a legend about the naming of the Karnafuli river. It says an Arakanese princess who fell in love with a tribal prince of Chittagong was once enjoying a moonlit boatride on the river with the prince. While admiring the reflection of the moon dancing on the rippled water surface, the princess inclined slightly and a flower tucked in the hair over her ear by the prince suddenly fell into the river. The princess was grief-stricken at losing the flower, which she held very dear as a present from her charming prince. She immediately jumped into the river to retrieve the flower but could not. Instead she was carried away by the fast-flowing current and vanished in the river. The prince dived into the river to rescue the princess but in vain. Out of sorrow he drowned himself in the river to unite with the princess after death. This tragedy gave the river its name Karnafuli from the word 'karnaful' meaning 'flower adorning the ear'. The river is known to the Marma tribe as the Kynsa Khyong. [Mesbah-us-Saleheen and Sifatul Quader Chowdhury]
See map in chittagong region river system.