Wearing goggles and a wet suit, the city leader swam breaststroke before immersing her face and beginning a front crawl.

Asked how she felt before taking the plunge in front of a large contingent of reporters, the mayor said: “Really good.”

Joining her for the swim was Paris 2024 Olympic president Tony Estanguet.

The clean-up of the Seine has been a long-term project with the goal of opening up the river for locals to swim in once the Olympics and Paralympics are over.

During the Games the open water swimming events – the marathon swim and the swimming phase of the triathlon – are scheduled to be held in the Seine. There is, however, a plan B – if the Seine does not pass water quality tests, the events will be held at the Vaire-sur-Marne water park.

Once the Games are over, the plan is to create multiple swimming areas along the river which will be open to Paris residents and visitors during the summer.

The Seine has been banned for swimming because of the poor water quality since 1924 – during that time numerous promises have been made to clean it up, but none have come to fruition.

Despite huge investment in the clean-up operation, doubt remain about water quality levels following periods of heavy rain or storms – when Paris’ ageing sewerage system often struggles to cope with the volume of water.

However tests done in recent weeks have shown that the water is safe to swim in.