Story highlights A day of mourning declared in Karelia on June 20

A total of 51 people were on three boats

(CNN) Thirteen children and one adult died Sunday after three tourist boats capsized during a storm in northwest Russia, officials said.

The three boats were carrying 47 children and four adults taking part in a camping trip when the boats capsized in a lake in the republic of Karelia, Russia's Investigative Committee said.

Russia's Emergencies ministry (EMERCOM) told state news agency RIA Novosti at least 36 people had been rescued.

Some of the rescued children are being treated at a local hospital for hypothermia, but they are expected to make a full recovery, emergency personnel said.

A day of mourning has been declared in Karelia on June 20 to honor the victims, officials said.

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