The death toll after two boats capsized on the River Sava in Slovenia rose to six on Friday, police said.
"At least six are dead while one person survived the accident," police spokesman Robert Perc told Reuters.
Another seven people are still missing after Thursday's accident.
The two boats, with 14 people aboard, overturned in strong currents near the Blanca hydropower plant, which is under construction 100 km (60 miles) southeast of the capital Ljubljana.
Slovenian media said one of the missing was Kristijan Janc, a member of parliament and mayor of the city of Sevnica, who organised the pleasure trip.
President Danilo Turk and Prime Minister Janez Jansa both visited the site of the accident overnight.
"This is a big tragedy ... the biggest that has happened on the water in Slovenia so far," Jansa told reporters.
Slovenia, a tiny Alpine state of 2 million people, declared independence from the former Yugoslavia in 1991 and joined the European Union in 2004.