It originates in the mountains of the Thanon Thong Chai Range, Khun Yuam District, Mae Hong Son Province, Thailand.

The river flows in a north–south direction and then in Sop Moei District it bends westwards and then northwestwards, forming a stretch of the Thai/Burmese border shortly before it joins the left bank of the Moei River, shortly before its confluence with the Salween.

[1] The Thai government, to solve persistent water shortages in the central region, have proposed a 70.7 billion baht plan to divert some 1.8 billion m3 of water annually from the Yuam River to the perennially-underfilled Bhumibol Dam.

As part of the plan, the Royal Irrigation Department (RID), would build 69 metre high dam with a storage capacity of 68.7 million m3 constructed on 2,075 rai of forest land, together with a pumping station on a separate 55 rai plot and a 61.5 kilometre-long tunnel passing through 14 villages.

ONEP rejected the EIA for the second time due to concerns about forest destruction, tunnel rock waste, and compensation issues.