Water from Laos’ dam breach streams into neighbouring Cambodia with floodwaters reaching 11.5 metres in some areas.

Phnom Penh, Cambodia – Thousands of people in northeastern Cambodia are being evacuated on Thursday as authorities scramble to cope with floodwater from the Xepian-Xe Nam Noy dam collapse in Laos that flowed south over the border.

Five billion cubic metres of water were released downstream when an auxiliary portion of the dam failed on Monday night.

On Tuesday, the Cambodian Ministry of Water Resources and Meteorology issued an alert “to be careful” in Stung Treng province along the Sekong River, a major Mekong tributary fed by the Xepian-Xe Nam Noy river system.

Since Tuesday night, some 1,200 families have been evacuated from four communes in the province’s Siem Pang district, according to Men Kong, a spokesman for the provincial government.

“They have been relocated to a safe place. There are 5,000 families in the whole district,” he said. “This water flow has affected the upper Sekong River, and will continue to [affect] the downstream regions.”

Provincial authorities called upon civil society groups to help distribute aid.

‘Safe places’

Authorities are concerned about the unpredictable rise in water levels on the Sekong River that is damaging infrastructure [Kry Solany/Al Jazeera]

Kry Solany of the My Village Organisation, a local rights and natural resource management NGO assisting in the delivery of clean water and food, expressed concern at the unpredictability of the situation as there was no clear evacuation plan in place beforehand.

“We don’t know where the safe places are for the people [to be evacuated]… We don’t know much from the authorities yet,” he said.

“Now in Siem Pang, it’s a declared flood zone as the water level has passed 11.5 metres in the Sekong River,” said Kry Solany, adding that by Thursday floodwaters will have reached the provincial capital, Stung Treng Town, some 100km south of the Laos border.

“The people in Stung Treng mostly live along the rivers, so when the water levels increase they will be affected,” he said.

‘Unpredictable rise’

Water Resources Ministry spokesman Chan Yutha said water levels continue to rise past 11.5 metres as about 200 soldiers and police have been dispatched to assist in evacuation efforts.

“We are concerned about the unpredictable water level rise,” he said.

The Mekong River Commission (MRC), an inter-governmental body that works with Laos, Cambodia, Vietnam and Thailand on the management of the Mekong River basin, in a statement on Wednesday predicted the provincial capitals of Stung Treng and Kratie downstream should be spared from potential flooding in the next few days, but said it would continue to closely monitor the situation.

The environmental trade-offs of hydropower development in the Mekong Basin have been the subject of much controversy, as the largely rural poor communities that depend on the waterways for fish have to cope with predicted declines in fish stocks of up to 40 percent.

Environmental groups have also long criticised the lack of transparency and community input in development plans in the region. The MRC has some oversight on the dozen hydropower projects on the Mekong mainstream, however, it has virtually none on the hundreds of tributary projects across the basin.

Additional reporting by Len Leng