Hong Kong, China (CNN) -- Dams have dried up in southwest China, Thai fishermen have almost completely stopped their fishery activities on the Mekong River, and nearly half of northern Vietnam's farmland is under threat because of a regional drought.
The region is facing water shortages and low water levels along the Mekong River -- particularly the tributaries that feed into it -- after a shorter-than-usual monsoon season last year and light rainfall in the dry season, affecting millions of people, livestock and hectares of land, and generating losses in the millions of dollars, officials from various countries and the United Nations say.
"This is a regional drought. It's not just restricted to one area. We expect it to go on now for maybe another two to three weeks before the rainy season starts, and then the water levels on the river will hopefully start to rise," said Jeremy Bird, chief executive officer of the Mekong River Commission, which was formed in 1995 by Thailand, Vietnam, Laos and Cambodia to oversee sustainable development along the waterway.
In southwest China, the drought has lasted for six months and is still spreading, resulting in an economic loss of more than $2.5 million in Yunnan province and leaving 19.4 million people facing a shortage of drinking water, according to a presentation made last week by Chen Mingzhong, deputy director general of China's Ministry of Water Resources, to a Mekong River Commission summit.
Less rainfall in the Mekong River basin led to a decline in water levels, with 662 rivers and water at 3,674 small dams drying up, Chen said in the presentation.
In Thailand, 7.6 million people and 59 of the country's 76 provinces have been affected by the drought, according to the Department of Disaster Prevention and Mitigation. The drought has been severe in the Southeast Asian nation, said Srisuwan Kuankajorn, co-director of the environmental nonprofit Terra in Thailand.
"According to villagers who live along the river in Thailand ... the Mekong is really drying. At some point, people seem to be able to even walk across the river, which has never happened before," he said Monday, adding that some locals have said they couldn't travel by boat or grow crops along banks of the rivers, and some reported cargo getting stuck.
People who live in the north, particularly Chiang Rai province, were in "big trouble," Srisuwan said, citing information received from local nonprofit groups. "They cannot fish. Fisheries are a very important source of income and source of protein ... they have almost completely stopped their fishery activities."
The Mekong is nearly 5,000 kilometers (3,100 miles) long, stretching from the Tibetan plateau, through southern China, and then along the borders of Myanmar, Laos and Thailand, through Cambodia to Vietnam. Some 60 million people live in the river basin, and Bird said the river's fisheries are the most productive in the world.
Forty percent of northern Vietnam's total farming area was under threat and 22 provinces on high alert for forest fires because of the dry conditions, according to the United Nations. Saltwater has also flowed into southern Vietnam's Mekong Delta in greater amounts than usual because of the low water levels, threatening rice and other crops on 620,000 hectares.
The mainstream Mekong in its upper reaches has now recovered from one-in-50-year low levels reached in February, but problems remain in tributaries that feed into the river, Bird said.
"Those are still running at extreme dry levels, the driest we have seen on record for the 50 years that we have been recording," Bird said. "It's really a question of very low water levels for communities, drinking supplies for agriculture, for livestock."
China's dams on the Upper Mekong Basin -- so far, three are operational and one is being filled with water -- have come under scrutiny amid the drought and river lows, with some critics questioning if Beijing was stocking up water in a bid to battle the drought in that country's southwest.
At the Mekong River Commission meeting last week in Thailand, Chen, the Ministry of Water Resources official, said his country was not to blame.
"The current extreme dry weather in the lower Mekong River Basin is the root cause for the reduced run-off water and declining water level in the main stem Mekong," he said in comments published by the Chinese state-run Xinhua news agency. "The hydropower stations built on the Lancang River (Mekong) will not increase the chance of flood and drought disasters in the downstream. Instead, it will considerably enhance the capacity of flood control, drought relief, irrigation and water supply for the downstream countries."
There are eight existing or planned Mekong dams in China's Yunnan province, and 11 proposed by Cambodia, Laos and Thailand are in various stages of research, according to the Mekong River Commission.
The commission was studying the influence of upstream dams in China, but past studies showed dams can have beneficial and detrimental effects.
For example, Bird said releases of water from dams upstream in China in early March this year helped keep water levels in northern Laos higher than they would have been in natural conditions and helped the upper reaches of the Mekong move from the one-in-50-year lows to one-in-10-year lows.
He also said China shared data at the meeting indicating that more water was being released from its dams rather than stored from December 2009 through March.
"We see the cause as extremely low rainfall, both at the end of the wet season and this dry season -- not due to dam operation," Bird said.
But for Srisuwan Kuankajorn of Terra, the dams are the main problem. He said villagers had detected fluctuations in water levels that they did not believe could be attributed to rainfall, rather thinking it was because of releases of water from dams by China.
"I don't ignore what the Chinese authorities are trying to say -- the drought, the low rainfall," he said, but added that China's actions had "been done without transparency, without taking into consideration the principles of sharing."
CNN Producer Kocha Olarn contributed to this report from Bangkok, Thailand