Early in January, locals in the northern Thai village of Chiang Khong woke to find the Mekong River had dropped a metre overnight.

Key points: Dams have been built along the Mekong River to generate renewable energy

Dams have been built along the Mekong River to generate renewable energy It has become a big problem for locals downstream, as it causes water levels to fluctuate dramatically

It has become a big problem for locals downstream, as it causes water levels to fluctuate dramatically Environmentalists say it is destroying migratory fish patterns in places where fish are the main source of income and protein

The water level fell so rapidly that damp mud was still visible days later when the ABC visited the area and some boats were left stranded on the riverbank.

"There were more than 10 boats stuck together because the water went down too fast," Chiang Khong boat driver Chaidin Chiablaem said.

"The rocks that we never see on the surface at this time of year — suddenly we saw them."

Locals in Chiang Khong in Northern Thailand say the water level should be far higher on the river bank at this time of year. ( ABC News: Amy Bainbridge )

Normally at this time of year, the Mekong slowly recedes until the tail end of the dry season hits in earnest around April or May.

But locals and environmental groups say China's Jinghong Dam, which generates hydropower 300 kilometres upstream, is causing dramatic fluctuations in river levels and changing the natural cycle of the river.

"I have been living here for 22 years, I have never experienced a situation like this," Chiang Khong Mayor Chalerm Tawiya told the ABC.

"It is so dry, that I have never seen so many rocks in the middle of the river, [as well as] the island, the sand dunes.

"The river wasn't even this low during the dry season."

Locals say rocks in the river are usually mostly submerged at this time of year. The dams combined with the drought, have made the water levels very low. ( International Rivers: Pianporn Deetes )

Why build dams along the Mekong?

The Mekong runs for more than 4,000km, starting in China and flowing through Myanmar, Laos, Thailand and Cambodia, before flowing out to sea in southern Vietnam.

Around 60 million people live on the river and derive an income from it in the Lower Mekong Basin countries.

It is a rich ecosystem with large migratory fish that move up and down the river to spawn, in sync with the wet and dry seasons.

"The fish in the Mekong River is the main source of income and the main source of protein for the rural populations along the Mekong Basin," Pianporn Deetes from International Rivers said.

Boat drivers are among those who notice the impact of the changing water levels in the Mekong River the most. ( ABC News: Amy Bainbridge )

"Not only in this part, but all the way to Laos, Cambodia and the southern part in Vietnam in the delta," she said.

But the river is increasingly used to generate renewable energy in the form of dozens of dams for huge hydropower projects.

There is growing alarm about the fate of the river's fish and the ecosystem they depend upon.

Dams have been built in the upper reaches of the river in China to supply hydropower to a nation hungry for more energy.

More dams have been built in Laos, for hydropower projects the Lao Government says will lift the nation out of poverty and make it the 'battery of Asia'.

Rocks can be seen along the edge of the Mekong River near the northern Thai village of Chiang Khong. ( ABC News: Amy Bainbridge )

The Jinghong Dam is not the biggest Chinese dam but it is its lowest on the river system and the closest to northern Thailand.

Environment groups say it is causing big problems for people living downstream, with China effectively controlling the flow of the river.

"The disaster to Mekong is not only from climate change but human creation, which is the dams," Niwat Roykaew, chairman of the Rak Chiang Khong Conservation Group said.

"Let's say the water level of Mekong is not seasonal anymore but depends on dam management upstream."

Health of Mekong disturbed 'devastatingly'

Residents say the water fluctuates quickly and they are worried dams are changing the river's natural cycle. ( ABC News: Amy Bainbridge )

Conservationists are worried that the rapid river level fluctuations could become a "new normal" for this part of the Mekong.

"The health and the ecosystem services of the Mekong River has been disturbed devastatingly," Ms Deetes from International Rivers said.

"It could be the new normal for the Mekong at this part, that the river is being controlled completely by the dams upstream."

"Already 11 hydropower stations have been built in the upper reaches in Yunnan province in China and control the water in the downstream, particularly this part of the river on the Thai-Lao border in northern Thailand," she said.

In late December, China announced testing at its Jinghong Dam would affect flows downstream in the Mekong and the Thai Government warned eight provinces to expect water levels to fall for several days.

But in a region already suffering a drought, locals and conservationists said China's apparent control over water flows was creating an unfolding ecological disaster.

"Definitely the drought is everywhere in the region," Ms Deetes said.

"What the dam has done to the Mekong River is it exacerbates the stage of this [drought].

"It makes things worse and it creates more impact on the communities and on the ecosystem."

'We don't see catfish anymore'

Fisherman Uthai Khampa said he sees far fewer fish in the Mekong River these days. ( ABC News: Amy Bainbridge )

There are growing concerns that dams in China, and further downstream in Laos, are destroying migratory fish patterns.

The ABC spoke to fishermen and other locals who said the once abundant catfish were no longer seen around Chiang Khong.

Fisherman Uthai Khampa, 60, is among those who believe catfish are already extinct in the Mekong River.

Fisherman Uthai Khampa is among those who believe catfish are already extinct in the Mekong River. ( ABC News: Amy Bainbridge )

"We don't see catfish anymore," he said.

"When water goes down quickly the fish are gone, it's not like the old times when water went up and down seasonally and naturally.

"I used to get fish every time I went out, but now I catch very little — just enough to eat but not to sell."

Local vegetable growers and river weed collectors also told the ABC it's becoming more difficult to make a living from the river.

Farmers along the Mekong River like Rattana Yongyuen are finding it difficult to make a living because of the water level fluctuations. ( ABC News: Amy Bainbridge )

Rattana Yongyuen, 56, gathers river weed to sell at markets and feed her family.

She has been collecting it since she was a child and says the water level fluctuations have been very unusual.

"If the water is fluctuating, I can't collect the river weed. If it is too low I can't take it because it is onshore.

"The income is much lower. I need at least 5 kilograms, but today I got nothing."

Working to get the balance right

The Mekong River Commission (MRC) is an inter-governmental organisation that works with the Thai, Cambodian, Lao and Vietnamese governments to jointly manage the sustainable development of the system.

The MRC's Anoulak Kittikhoun told the ABC there will be consequences if the natural regime of the river is modified.

But he is pleased China is now notifying downstream countries if flows are going to impact the river level.

"2019 was a critical year of drought but also because of some operation of dams, but we have to work with member countries in terms of sharing more information about their operation," Dr Kittikhoun said.

"Increasingly, China especially notified [us] more and more of their operations before they happened, so I think this is an improvement from the past.

The Mekong River provides a fertile base for local agriculture. ( ABC News: Amy Bainbridge )

"In terms of the broader impacts, of course when you modify the natural regime there will be consequences.

"But we have now agreed with the Lancang-Mekong Water Centre to jointly study the cost, the exact impact and [have] them recommend certain measures to the governments of the six countries to address, including any concerns by the local people."



Neither the Chinese Ministry of Water Resources or the National Energy Administration responded to requests for information about the Jinghong dam.

The sand banks along the Mekong River are larger than normal with water levels significantly down. ( ABC News: Amy Bainbridge )

But last year, the Chinese embassy in Thailand said its dams were helping to regulate flows during the wet and dry seasons.

"Frequent floods and droughts in the Mekong basin are the effects of global climate change," it said.

"The construction of cascade reservoirs on the Lancang River is an effective measure against climate change.

"The cascade hydropower stations which discharge water in the dry season and store water in the wet season, are able to help adjust the water level of the Lancang-Mekong River."