It is in a constricted coastal region in southeastern Myanmar (formerly Burma), which borders Thailand on the east and the Andaman Sea on the west.

[8] From here, it flows 33 mi (53 km)[9] before reaching the Andaman Sea at the major seaside town of Myeik (Mergui), situated on a small island that is formed by two branches of the river.

[14] The tributaries include Tonbyaw Creek,[15] Thuggoo River,[16] as well as the Hti-phan-ko stream on the Great Tenasserim's right bank.

[4] tributary [2] In the late 18th century, during the wars on territorial dispute between Myanmar and Thailand, the Great Tenasserim River region came under the control of the Burmese.

[4][11] The main agricultural operations in the Tenasserim River valley include paddy rice, mostly near Tavoy; vegetables, coconuts, rubber, and teak.

[8] Tin as a mineral (a dioxide), in the Mergui and Tavoy districts of the valley, is extracted from the pebbles found in the river.

Lead has also been found in the valley at Toungoo, and at the mouth of the river on Maingay Island in the Mergui Archipelago, which is yet to be extracted.

[22] The state-run New Light of Myanmar newspaper claimed that a signing ceremony for the Tenasserim Hydropower Project was held on October 9, 2008, between the Burmese Ministry of Electric Power No.

1, the Italian-Thai Development Public Co. Ltd., of Thailand and Singapore's Wind Fall Energy Services Ltd.[22] The Burmese military and Thai officials took water levels in December 2008.

A Thai expert has been hired to take water level measurements of the river in different areas in different seasons to assess the best location for a dam.

[22] A new fish species of the true loaches family was captured for the first time in the Great Tenasserim River in 1993, and was named "Kamphol Udomritthiruj" after the person who found it.

[23] Although it is considered a suitable aquarium fish, the Emperor loach has not been exported from the area due to a serious insurgency problem prevailing in the region.