The floodgates of the largest and most controversial dam project in the country’s history officially closed yesterday at an inauguration ceremony presided over by Prime Minister Hun Sen, who took aim at environmentalists, ambassadors and NGOs in a wide-ranging speech.

During his one-hour address, the prime minister said the Lower Sesan II Dam, near the border with Laos in Stung Treng province, would lower electricity costs and put the Kingdom on its way to hooking up every village in the country to the electricity grid by 2022.

“There is no development that doesn’t have an effect on the environment,” Hun Sen said. “It’s just a matter of more or less. But it requires consideration of whether we should or should not do it.”

The dam’s first turbine is expected to begin generating electricity by the end of November, with the rest expected to be fully operational by 2018.

A joint project between China-based Hydrolancang International Energy, Vietnam-based EVN International and Cambodia’s Royal Group – chaired by Oknha Kith Meng – the dam will be privately operated before being handed over to the government after 40 years.

The Ministry of Mines and Energy said yesterday that the company will sell the electricity at a fixed rate of $0.07 per kilowatt hour, significantly less than national rates currently as high as $0.20.

However, the $800 million, 400-megawatt dam was controversial from the start, drawing protests from displaced locals and raising alarm among environmental experts.

Hun Sen dismissed those environmental concerns yesterday, criticising “radical environmentalists” and pointing out the explosive demand for energy in Cambodia, which has the most expensive electricity in the region.

“[Mother Nature] keeps causing problems on every issue,” he said, referring to the recently dissolved environmental NGO. “If you do like this, how can we develop? We cannot do this or that. Coal and kerosene production, they said that it creates smoke. Producing electricity, it affects the environment.”

In response, Mother Nature co-founder Alejandro Gonzalez-Davidson called the prime minister’s comments “disconnected from reality”.

In his speech, the premier also took a shot at an unnamed diplomat who he said tried to persuade him to nix the Sesan dam project years ago due to its impact on fisheries.

“I was surprised because apparently Cambodian fish can climb trees and mountains,” the prime minister joked. “My country’s fish live in the Tonle Sap and Mekong River. They do not live in the Sesan River.

“After construction, just release more fish [into the river],” Hun Sen added.

Despite the premier’s assessment, fish experts have long warned about damage to migration routes. Ian Baird, a geographer at the University of Wisconsin who studies Mekong River fisheries, said fish rely on the ability to move between the Sesan and Srepok rivers and the Tonle Sap to breed.

According to Baird, the negative impacts of the Sesan dam will be felt in Laos, Thailand and Vietnam, all of which depend on the Mekong River system’s annual flood cycle to deposit nutrient-rich soil on its banks. The dam will also prevent fish from migrating upstream to Cambodia’s northern neighbours.

“It is a very sad day for Cambodia today,” Baird said.

The dam has already displaced around 1,500 households and flooded tens of thousands of hectares of forest in Stung Treng’s Sesan district.

Roughly 100 families in Sre Kor and Kbal Romeas villages who have refused to relocate remained defiant yesterday.

“Our stand remains the same,” said Srang Lanh, 49, an ethnic Phnong woman from Kbal Romeas. “We do not want electricity. What we want to do is to agree to live at the old location . . . The dam separates us and causes difficulties for us every day.”

Other villagers who agreed to move to the resettlement site along National Road 78 said they are enjoying access to better roads and electricity – provided by nearby Laos, not from the Sesan dam – but are adjusting to the need to purchase fish and water that was once supplied by the river.

“I agreed to leave because the country is developing,” said 68-year-old Sa Phorn, who said he was one of the first villagers to leave Kbal Romeas. “We need electricity.”

But ecologists and water management experts remained concerned that the negative impacts of the Sesan dam will outweigh the benefits. Hydroelectric projects, largely funded by the Chinese, are springing up along the Mekong River and its tributaries across the region.

If approved, two other projects in discussion – a 900-megawatt Stung Treng dam and the 2,600-megawatt Sambor Dam in Kratie province – would dwarf the Lower Sesan II Dam. Both projects are also backed by Meng’s Royal Group.

“The direct impact of one dam is small, but collectively they will change the way water and sediment flow in the Mekong River,” said Jamie Pittock, a freshwater ecologist at Australian National University who researches the impact of Mekong dams on fisheries.

The Mekong River Commission, an intergovernmental body that monitors the river’s development, is expected to finish a study on the dams by the end of the year. Portions of the study released last year estimate that the economic damage to Cambodia from 11 dams proposed on the Lower Mekong could amount to $450 million per year and cut the fisheries yield in southern Cambodia in half.

However, Fisheries Action Coalition Team Director Om Savath said government authorities have largely ignored pleas from researchers and environmental activists.

“We don’t believe the economic growth related to the hydropower dam will make things better for the fishermen living along the river or the Cambodian people,” Savath said. “Investors will get the benefit.”