The event, organized by the women's community group Smile 13
, is restricted to women wearing all-over swimming outfits "covering body parts from breast to knees" -- often referred to as a "burkini."
Boys under 10 are also allowed to attend the day at Speedwater Park near Marseille on September 17.
"The goal of the burkini is precisely not to tempt since it's a loose outfit," said Smile 13 on its Facebook page
, adding that there will still be male lifeguards present at the park.
"Women wandering around in bikinis are more at risk for rape that's for sure," it continued.
Burkini day sparks criticism
The comments were criticized by Stephane Ravier, mayor of the 7th district of Marseille and member of the far-right Front National party.
"For the organizing association, not wearing a 'burkini' encourages rape... Typical Islamist speech!" he tweeted.
Similarly, Valérie Boyer -- who represents the Bouches-Du-Rhone region as a member of the center-right Les Republicains -- said in a statement: "Burka, chador, abaya, niqab, hijab, the name doesn't matter -- they constitute a confinement of the gender, a negation of the person, a prohibition of liberty, a prohibition equality, a prohibition of fraternity."
France's burqa laws
In April 2011, France became the first European country to ban wearing in public the burqa, a full-body covering that includes a mesh over the face, and the niqab, a full-face veil with an opening for the eyes.
Those breaking the law
face fines of 150 euros (about $205) or public service duties.
The law was upheld by the European Convention on Human Rights in 2014
, after a 24-year-old woman brought the case to court, claiming it infringed on her religious freedom.
The government also previously banned Muslim headscarves
and other "conspicuous" religious symbols in French schools, in February 2004.
The laws have been criticized by religious freedom advocates but supported by others who see the Islamic veil as demeaning to women and inconsistent with France's rigorously enforced secularism.
Is it legal?
As the burkini day is a private event, it is also deemed legal.
But that hasn't stopped Michel Amiel, Mayor of Pennes-Mirabeau, from issuing an order to the prefect forbidding the event as it could lead to public unrest, in comments made to French newspaper Le Parisien.
He told the newspaper that if the prefect found his order was not legal, he would refer it to France's Administrative Court.