Four of the world’s 10 largest freshwater fish migrate up the Mekong River to spawn, yet the lives of these big fish—which can grow to be the length of a four-door car and weigh over 1,300 pounds—are at risk should a hydropower plant be built on a stretch of the river in northwestern Laos.

The Laotian government wants to build a 1.26-gigawatt plant on a main artery of the lower Mekong River at Xayaboury near the Thailand border. The government submitted its plans in September, saying the dam would generate foreign exchange income since 90 percent of the electricity would be sold to neighboring Thailand, Vietnam and Cambodia.

However, a recent environmental assessment by the Mekong River Commission (MRC) recommends that the building of the dam be halted for 10 years. The MRC is an organization established by Thailand, Cambodia, Vietnam and Laos for the joint management and sustainable development of river resources.

The 200-page report says: “The mainstream projects are likely to result in serious and irreversible environmental damage, losses in long-term health and productivity of natural systems and losses in biological diversity and ecological integrity.”

Even before the MRC assessment, environmental groups such as the World Wildlife Fund (WWF) opposed the plan for the dam because of the threat to wildlife and the migration patterns of endangered freshwater species, including the Mekong giant catfish and the enormous Mekong stingray. “It is already very clear this dam would amplify and accelerate the negative impacts of Chinese dams to the Mekong delta. What are the other impacts?” said Marc Goichot of the WWF in an article by the Guardian.

Alongside the threat to wildlife, local villagers living along the river would be displaced from their homes once construction on the proposed dam starts. As many as 2,130 people from 10 villages would have to move to another location if dam construction starts. Most of these villagers earn their living from fish harvesting and agriculture.

In an article for The Nation, one villager states that a Thai construction company inspecting the site told local residents that their houses would be rebuilt at another location and that the company would build a road, as well as provide water and electricity. Villagers who own teak farms were told that they would be compensated 150,000 Lao kip (1.8 US dollars) per piece of teak. Another villager said the company staff told them that they would build a special channel for boat traffic.

The dam in question is one of a dozen mainstream dams planned along the lower Mekong, 10 of them in Laos. According to a news report by the Australian Broadcasting Corporation, the MRC’s strategic environmental assessment (SEA) acknowledges that Laos, one of the poorest countries in Asia, could earn billions of dollars annually if these dams are built. However, the SEA also predicts that fisheries could lose $476 million a year and “in the short to medium term, poverty would be made worse by any of the mainstream projects, especially among the poor in rural and urban areas.” Furthermore, the report predicts that environmental damage would be severe.

During the 10-year deferment period, the Mekong River Commission recommends that the government work with multilateral development banks, developers, and the MRC itself to identify innovative ways of using the power of the Mekong River in ways that do not involve building dam after dam across the breadth of the river.