Laos inaugurated the construction of a controversial dam on the Mekong River on Wednesday, despite comments from the country's prime minister that the project had been delayed. “We held the groundbreaking ceremony today,” said Rewat Suwanakitti, the deputy managing director of Xayaburi Power, the company leading the project. “The Lao authorities told us that we could begin construction.” The project is the first in a series of dams planned for the lower Mekong River and comes amid concerns by scientists and countries that share the river that the dam will irreparably harm fish stocks, which are an important food source for millions of people. Electricity produced by the Xayaburi dam, which is named after the province in Laos where the project is, will be sold to Thailand. Officials from the Laotian government say they are counting on billions of dollars in revenue. The prime minister of Laos, Thongsing Thammavong, told The Wall Street Journal on Tuesday that the project was awaiting further study. But at the dam site, preliminary work has already reached an advanced stage. The Thai construction company charged with building the dam, CH. Karnchang, has spent the past two years carving roads through the jungle to the remote site and putting equipment in place. The groundbreaking ceremony on Wednesday included senior officials from the Laotian government and diplomats from Vietnam and Cambodia, Mr. Rewat said.