Two Cambodian environmental activists were reportedly detained by Lao authorities yesterday while photographing construction of the Don Sahong dam near the border with Cambodia’s Stung Treng province.

According to Se Seamdy, the leader of Youth for Social and Environmental Protection, the organisation to which the two activists belong, brothers Chum Huor and Chum Huot were on a boat with two other people when they were arrested and questioned for over an hour before being released.

“One of them got sick because he was so afraid,” he said.

While Seamdy denied media reports that the phones and cameras carried by the brothers had been destroyed by Lao authorities, Adhoc provincial coordinator Hou Sam Ol said yesterday that the devices had sustained water damage and were no longer functional. Seamdy declined to elaborate further on the circumstances of the detention, while Sam Ol said he had been told “that their phones dropped into the water, but it is not clear what caused that”.

In social media posts Huor and Huot appear carrying campaign banners that read “Together protect the environment”, and “Having Don Sahong means there is no dolphins”, referring to the endangered Irrawaddy river dolphins that inhabit stretches of the Mekong in Cambodia, and which experts warn may be eradicated by the dam’s construction.

The Mekong River Commission (MRC) – the international body responsible for mediating disputes over the Don Sahong between Laos, Thailand, Vietnam and Cambodia – has lost more than half of its funding for 2016-2020 compared with the last five years. What’s more, repeated requests to the Lao government for environmental impact assessments and scientific studies on the consequences of the Don Sahong through the MRC have been denied as the commission requires the consent of the Lao government.

Several studies have predicted significant losses in fish populations if the dam construction, which began in late 2015, moves forward. According to research presented in October at the Greater Mekong Forum on Water, Food and Energy in Phnom Penh, the Kingdom may lose up to 100 per cent of its migratory fish population as a result of Mekong river dam projects in Lao and Cambodia such as the Don Sahong.

Neither the Cambodian embassy in Laos nor a spokesman for the Ministry of Foreign Affairs could be reached for comment yesterday.

Mom Saroeun, Stung Treng provincial governor, speaking yesterday, said he was unaware of the incident.