Five people in their 60s and 70s died in Hérault, while two aged 58 and 71 died in Bouches-du-Rhône. Another two died in Leucate, Aude.
The weather caused the seas to swell, creating choppy waters which led to them being swept out.
France has been hit by a heavy storm over the week, with record-breaking rainfall and yellow weather warnings throughout the south.
Much of southern France was placed under orange weather alerts – the second most serious indicating the need to be “very vigilant”.
Thunderstorms, rains and floods hit on September 14 and 15, leaving lorries tilted and stranded in high water.
Police officers in Hérault also evacuated beaches.
Vias also saw one man drown after reportedly falling from rocks into the waters.
Jordan Dartier, mayor of Vias, told French broadcaster LCI: “I cannot understand how people got into the water when the seas were rough.
“It’s a dramatic day for our region.”
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Grégory Coutarel, head of search and rescue in Bouches-du-Rhône, told the BBC warm temperature of the water had tempted people to swim, even though conditions were not ideal.
He said: “On weekdays, enjoying the sea at 24C is quite exceptional, and can tempt tourists.”
He added that, as the weather stays warm for longer, lifeguards should be kept in place “until the end of September or even until mid-October”.
Local fire chief Aurélien Manenc also told broadcaster TF1 people do not understand how dangerous choppy waters can be.
He said: “The water is warm, you think you are going to have fun – and quickly you are pulled towards the open sea and towards the bottom, and you get exhausted trying to come back.
“This is what causes drowning.”
It comes as Gard, Hérault, Ardèche, Isère, Drôme, Savoie, Haute-Savoie and Ain remain under a yellow alert – urging vigilance – along with 30 other southern and eastern departments.
Authorities have warned people should be “aware” of the weather conditions and perhaps avoid any activities that may put them at risk during a storm.
As of 10pm local time (9pm BST) on Wednesday, Gard’s firefighters had carried out 1,280 operations linked to the storms, including 57 airlift rescues and 86 other rescues.
Crews were particularly busy in the south of the department and around Nîmes.