Mekong, whose water level has dropped to only 33 centimeters, the lowest in 50 years

A Cambodian farmer ploughs a field during the dry season in Kandal province, on the outskirts of Phnom Penh, March 18 ,2010. Severe drought has hit Southeast Asian countries, parching the region's major river, Mekong, whose water level has dropped to only 33 centimeters, the lowest in 50 years. Apart from the drought, villagers who live along the Mekong, which flows 4,350 km (2,700 miles) from the glaciers of Tibet to the rice-rich delta of southern Vietnam, attributed the falls of water level to newly constructed dams in China. REUTERS/Chor Sokunthesa

A Cambodian farmer collects water for his crops during the dry season in Kandal province, on the outskirts of Phnom Penh, March 18 ,2010. Severe drought has hit Southeast Asian countries, parching the region's major river, Mekong, whose water level has dropped to only 33 centimeters, the lowest in 50 years. Apart from the drought, villagers who live along the Mekong, which flows 4,350 km (2,700 miles) from the glaciers of Tibet to the rice-rich delta of southern Vietnam, attributed the falls of water level to newly constructed dams in China. REUTERS/Chor Sokunthesa

A Cambodian man collects water for domestic use during the dry season, from a river in Kandal province on the outskirts of Phnom Penh March 18 ,2010. Severe drought has hit Southeast Asian countries, parching the region's major river, Mekong, whose water level has dropped to only 33 centimeters, the lowest in 50 years. Apart from the drought, villagers who live along the Mekong, which flows 4,350 km (2,700 miles) from the glaciers of Tibet to the rice-rich delta of southern Vietnam, attributed the falls of water level to newly constructed dams in China. REUTERS/Chor Sokunthesa

A man and his dog walk on the river bed of the Mekong river at Koh Dach district in Kandal province, east of Phnom Penh, March 17, 2010. Changing weather patterns and rising seas are already affecting many people in Southeast Asia's Greater Mekong Basin and climate change threatens the livelihoods of millions more, a report by global conservation group WWF released in October 2009 shows. REUTERS/Chor Sokunthea

A dog wades in the Mekong river at Koh Dach resort in Kandal province, east of Phnom Penh, March 17 ,2010. Changing weather patterns and rising seas are already affecting many people in Southeast Asia's Greater Mekong Basin and climate change threatens the livelihoods of millions more, a report by global conservation group WWF released in October 2009 shows. REUTERS/Chor Sokunthea

Cambodia fishermen work on their fishing boat on the Mekong river in Phnom Penh March 17, 2010. Changing weather patterns and rising seas are already affecting many people in Southeast Asia's Greater Mekong Basin and climate change threatens the livelihoods of millions more, a report by global conservation group WWF released in October 2009 shows. REUTERS/Chor Sokunthea

A fisherman rows his boat along the Mekong river in Phnom Penh March 17, 2010. Changing weather patterns and rising seas are already affecting many people in Southeast Asia's Greater Mekong Basin and climate change threatens the livelihoods of millions more, a report by global conservation group WWF released in October 2009 shows. REUTERS/Chor Sokunthea