At Khong Chiam the Mun river, the biggest river of the Khorat Plateau, joins the Mekong, which forms the north-eastern boundary of Thailand with Laos. It is called Maenam Song Si or the Mun River alluvium because the brown water from Mekong River is mixed with blue water from Mun River. It is located about 84 km. from Ubon Ratchathani City centre.
The area where the borders of the three countries Thailand, Laos and Cambodia meet is promoted as the Emerald Triangle, in contrast to the Golden Triangle in the north of Thailand. The Emerald refers to the large intact monsoon forests there.