A substantial majority of the people who live along the Mekong River are engaged in agriculture, and rice is the major crop. The heaviest population concentrations are in the delta and on the Khorat Plateau. The small urban population has been growing rapidly, chiefly through migration to the capital cities.

Mekong River People

Mekong River Kid

The peoples of the basin are diverse. Most residents of the uppermost Mekong Valley are Tibetan. South of the Tibetan Highlands, the peoples of the river basin fall into two broad cultural groupings. The hill peoples subsist mainly through shifting cultivation, and have traditionally formed small, kin-based social units, while the lowland peoples, who practice sedentary agriculture, have formed complex state societies. The hill peoples speak languages belonging to five different language families: Tibeto-Burman (including the Yi, Hani, and Lisu of Yunnan), Tai (including the Shan of Myanmar and the so-called Black Tai and Red Tai of Laos and Yunnan), Hmong-Mien (including the Hmong of Laos and Yunnan), Austronesian, and Mon-Khmer (including the diverse Montagnard peoples of Vietnam). The lowland peoples, however, form the majority of the population, and most belong to one of the dominant ethnic groups of the region’s nations. These include the Han Chinese of Yunnan, whose language is distantly related to the Tibeto-Burman languages, the Lao of Laos and the Thai of Thailand, both speaking languages in the Tai family, and the Vietnamese of Vietnam and the Khmer of Cambodia, Vietnam, and Thailand, both speaking Mon-Khmer languages. The Cham, a minority lowland people of Vietnam and Cambodia, speak an Austronesian language.
Source: britannica.com