Nine people died in violent storms that swept France overnight and today, and fears of falling trees forced Paris to close its parks and cemeteries, interior ministry and other officials said.
Rescue services backed up by helicopters searched for three more missing people amid complaints that holiday-makers had ignored red warning flags alerting them to the dangers of heavy seas, flooding and gale-force winds.
"The recklessness of some swimmers and the foolhardiness of others has resulted in a dramatic death toll," said Mr Eric Soupra, spokesman for the Interior Ministry's civil emergencies service.
"The red flag signifies an absolute ban on swimming. The respect of these elementary rules would allow us to dramatically reduce the number of drownings suffered each year," added junior transport minister Mr Francois Goulard in a statement.
Around a quarter of metropolitan France's administrative districts were affected by the bad weather.
Some 1,000 people were evacuated overnight from a campsite in the southeastern Ardeche region, where an estimated 3,000 homes were still without power supplies by nightfall.