"Canua Island", a 1,750 square-metre (18,800 square feet) motorised platform boasting a restaurant, bar lounge and freshwater swimming pool, was inaugurated Thursday night off Mandelieu-La Napoule on the Cote d'Azur in southeastern France.

The luxurious two-storey platform set on a trimaran and anchored 600 metres from the seafront can accommodate up to 350 people.

Opponents of the 16-million-euro project have denounced it as "an ecological aberration".

Environmental groups have long battled for increased protection for sea life and the coastline of the highly developed Cote d'Azur, long considered a playground for the rich and famous.

The owners were denied permits to operate last year, but they took the case to court and were granted an authorisation to launch the project.

The project had initial support from just one local commune, Mandelieu-La Napoule, but was contested by the head of the broader Provence-Alpes-Cote d'Azur region, Renaud Muselier, a member of President Emmanuel Macron's ruling party.

On Friday, around 20 mayors, including those of Nice and Toulon, signed a letter denouncing "this commercial exploitation of the marine environment".

But the owners stress that the project is safe, with the engines running on biofuel, a desalination system producing freshwater and all waste being recycled on land.

Due to the controversy, the floating beach will not be open to the public this season.

Based at La Seyne-sur-Mer, near Toulon, it will be available for private events such as weddings on the Cote d'Azur. The owners have already received around 30 booking requests.