A group of environmental activists petitioned the government yesterday to release information about the potential impact of the proposed 2,600-megawatt Sambor dam on the Mekong River in Kratie province, which they say could displace thousands and destroy ecosystems.

Speaking after submitting the petition to the Ministry of Environment, Chum Hour, a representative of the youth group Social and Environmental Protection Youth (SEPY), said 20,000 families would be evacuated and 70,000 hectares of land flooded if the dam was completed.

“It would be the largest dam in Cambodia,” Hour said. “We are concerned that people will be evicted and that [local freshwater] dolphins will become extinct . . . we want to know if the project will really happen or not.”

Aside from SEPY, the petition was signed by the Khmer Student League Association and the environmental non-profit Mother Nature. The three organisations claim that a government-sponsored environmental impact assessment has already been completed and that the government is withholding the information.

However, Meng Saktheara, spokesman for the Ministry of Mines and Energy, said yesterday that the dam proposal was still being studied. He said the government had contracted an organisation called NHI to carry out a study on the social and environmental impact of the proposed dam, but said he was unable to remember what “NHI” stood for.

Independent hydropower consultant Hen Oudom, however, said that the US-based Natural Heritage Institute was responsible for the study, adding that the results had not been finalised.

Chea Phallika, a consultant and former employee at the NGO Forum, said an Australian environmental consultancy, ICEM, had conducted an independent assessment of 12 proposed mainstream dams on the Mekong River and advised the government not to move ahead with the Sambor dam without further assessment.

Both Oudom and Phallika expressed concern over the environmental impact of the proposed dam. “I am concerned about ecosystems being destroyed and water flows changing . . . and a lack of transparent information,” Oudom said, adding that he had heard rumours the NHI assessment would be completed in November.

Chan Sar, a villager living on Rongeav island in Sambor district, said yesterday that he was concerned his home would be submerged if the project went ahead. “We are afraid of losing our homes, our culture, our jobs,” Sar said. “If we are evacuated, we don’t know what we’d do.”

In the meantime, concerned local communities have asked activists to speak out on their behalf. “They told me that a Chinese company went to assess the area,” said Mory Sar, of the Cambodian Youth Network.

Information published by the organisation International Rivers suggests that two Chinese companies, China Southern Power Grid Company and China Guodian Corporation, carried out feasibility studies for the project between 2006 and 2010.

The Ministry of Environment and NHI could not be reached for comment.