Ljubljana- Slovenian rescuers were searching for bodies in the Sava River Friday, a day after a freak accident at a poorly organized boating event claimed the lives of a dozen people.

Eight people from the two canoes which capsized Thursday afternoon were confirmed dead, including Kristijan Janc, the mayor of Sevnica, a town 70 kilometres southeast of Ljubljana who organized the event, police said. Janc was also a lawmaker in the national parliament.

Four others were still missing, their chances of survival described as "negligent."

Janc's plan was to paddle downstream before a new hydro electric plant at Sevnica became operational, effectively closing the river. The tragedy occurred when the two boats went over the threshold of the dam and down a concrete slope.

Only two passengers from the two canoes survived, one of them reportedly Janc's wife.

Another canoe capsized earlier and all from it swam to safety, while a fourth canoe, with a TV cameraman, stopped in time to remain safely upstream of the dam.

It remains unclear why the two canoes taking part in Janc's event, dubbed "The Last Ride," approached the dam and the two-metres slope, as well as why none of the passengers wore life vests.

The video recording, aired by Slovenian national television, shows one of the boats approach the edge despite cries of warning, before tipping nose first and disappearing. It appears the victims drowned in the vortex at the bottom of the two-metre concrete slope.

The water is 6 metres deep there, accelerated and swirling as it gorges through dam door and down the short slope. A shaken witness from another canoe told an empty canoe bobbed up and down for a long time in place, held there by the current.

The search effort, covering an "aquarium" only 5,000 metres-square in area, is hampered by poor visibility in the water, which is said to be only 20 centimetres. Slovenian President Danilo Turk and Prime Minister Janez Jansa visited the scene of the tragedy Thursday night.

Slovenia is the most-developed former Yugoslav republic, which split from the federation in 1991 and joined the European Union and NATO in 2004. (dpa)