MOSCOW (AP) — At least 13 children and their adult instructor have died in a storm while boating on a lake in Russia’s northwestern region of Karelia, officials said Sunday.

Vladimir Markin, a spokesman for the nation’s main state investigative agency, said several boats with children overturned Saturday in a storm in Syamozero, 120 kilometers (75 miles) east of the border with Finland.

Of 47 children and four adult instructors in the boats, 13 children and one adult have died, Markin said.

Markin said an instructor has been detained as part of an official probe, suspected of violating safety rules, and a search for two other suspects is underway.

The children who went out boating came from Moscow and the capital’s mayor, Sergei Sobyanin, offered condolences to the victims’ families.

Repeated warnings of an advancing Atlantic cyclone had been issued days ahead of the storm, advising everyone against boating on the lake, one of the favorite holiday destinations in the area, regional Karelia lawmaker Alexei Gavrilov said on Rossiya 24 television.

“They didn’t have the right to go out boating,” he said.

Vladimir Kucherenko, the director of a local tourist company, said that most children had apparently died from long exposure to cold water, as water temperatures in the lake were 8-10 degrees Celsius (46-50 Fahrenheit). He said strong winds might have driven boats across the lake, making it hard for the children to get to the shore.

“I would like to look the person who allowed them to go boating in the eye,” Kucherenko said in televised remarks. “It was suicidal.”

Local experts said that the shallow lake could be extremely dangerous to navigate in strong winds, and even experienced local fishermen stayed away from the lake over the weekend.