Meghna , river, c.130 mi (210 km) long, formed at the outlet of the Surma valley, NE Bangladesh, by the branches of the Surma River. It flows south, receiving arms of the Ganges and Brahmaputra rivers, to the Bay of Bengal. The Meghna is an important inland waterway, navigable throughout its length by river steamers, although hazardous due to its high speed. In the springtime, at high tide, tidal bores, c.20 ft (6.1 m) high, rush upstream with great destructive force.

Ganges river dolphins are found in the Ganges, Meghna and Brahmaputra river systems of western India, Nepal, Bhutan, and Bangladesh and the Karnaphuli River, Bangladesh. Discontinuous distribution from the foothills of the Himalayas to the limits of the tidal zone.

During the dry season, when the river levels are low, the adults tend to stay in the main river channels. During the monsoon season, they move into creeks and tributaries. Some juveniles rarely leave the tributaries. There are usually more dolphins at junctions where 2 rivers meet, and just downstream of shallow water. They prefer deeper water, but can be seen in water as shallow as a metre. The building of dams prevents Ganges river dolphins from following migration routes that they may have previously taken.

Platanista Gangetica (Latin Name) probes the mud in river bottoms with its long snout in search of shrimp and fish. They swim all day and all night and continually emit sounds. One study showed that 81% of the sounds are echolocation and 5% communication. Echolocation is used by the dolphins in foraging and it helps these animals to sense objects; they can detect a wire one millimeter in diameter.