Local children play in the Mekong River in Chiang Khong, Chiang Rai, in Northern Thailand, in this handout. Greenpeace photo taken 17 March 2010. According to Thai autorities, the region most important river reached its lowest levels in 20 years last week. China has since released water from its upstream dams. The UN World Water Day celebration on monday next week comes amidst a massive drought in Southeast Asia that is affecting water sources in Thailand, Vietnam, Cambodia, Laos and the Philippines.