At Khong Chiam the Mun River, the biggest river of the Khorat Plateau, joins the Mekong, which forms the northeastern 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 about 84 km (52 mi). from Ubon Ratchathani city centre