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Lower Salween (Burma and Thailand)

In Burma the Salween river is officially known as Thanlwin; in Shan State, which the river enters immediately upon leaving China, it is also known as Nam Khone. Turning south, the river slices a winding course through the vast upland region known as the Shan Hills. This area is characterized by a complex, broken topography of small mountain ranges, plateaus and cliffs, through which the Salween has cut an extensive series of gorges. As the Salween flows south and descends in elevation, it travels from temperate to subtropical and finally tropical climate zones, with yearly precipitation ranging from 1,200 to 2,000 mm (47 to 79 in) in the Shan Hills area. The total length of the river in Burma and Thailand is 1,316 km (818 mi).

In Shan State and Karenni State (Kayah State) the river is joined by several large tributaries, including the Nanding River and Hka River from the east, and the Pang, Teng, and Pawn Rivers from the west. The Pang River is noted for its extensive limestone formations near the confluence with the Salween, where it breaks into a myriad of cataracts, channels and islets known as Kun Heng, "Thousand Islands". Inle Lake, the second largest lake in Burma and a World Biosphere Reserve, drains into the Salween by way of the Pawn River.

Further south, the river enters Karen State (Kayin State) and forms the border between Burma and Thailand for about 120 km (75 mi). In Thailand the river is known as Salawin; much of the Thai side of the border is part of Salawin National Park and the Salawin Wildlife Sanctuary. At the south end of the border section it is joined by the northwest-flowing Moei River, which forms the Burma–Thailand border south of this point. In Karen State, the river flows through karst limestone hills where numerous caves and unusual rock formations line the banks, particularly around the city of Hpa-An.

The Salween emerges from the mountains into the coastal plain near Hlaingbwe Township. Near the coast, annual rainfall is as high as 4,000 to 5,000 mm (160 to 200 in), supporting dense tropical rainforest as well as a productive rice industry. The river flows for a further 100 km (62 mi) before terminating at a modestly sized delta and estuary in Mawlamyine in Mon State. The Salween is tidally influenced up to 75 km (47 mi) inland. Here it is joined by the Gyaing River from the east and the Ataran river from the southeast. The Thanlwin Bridge, the second longest bridge in Burma, connects Mawlamyine to Mottama. The combined river then breaks into the Dayebauk (north) and Mawlamyine (south) channels, forming Bilugyun Island before emptying into the Gulf of Martaban.