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There's only a year to go until the Paris Olympics and preparations are well under way to welcome athletes and spectators.

Host cities typically make a big effort to clean up their appearance as all the cameras will be focused on them for the famous sporting event.

In Paris they've been working hard to clean up their dirty river, the River Seine, which flows through the heart of the French capital.

For 100 years swimming was banned in the river because of the levels of water pollution that could make people ill.

But after years of work, and more than 1.4 billion euros (£1.2bn) of investment, the Seine is going to be ready to welcome swimmers and divers back once more.

It will play host to three Olympic events - triathlon, marathon swimming and paratriathlon.

There will also be three open-air swimming areas by 2025, for everyone to enjoy.

"When people see athletes swimming in the Seine with no health problems, they'll be confident themselves to start going back in the Seine," says Pierre Rabadan, the city's deputy mayor, who is also overseeing the Paris Olympics.

The problem was, for years industrial waste poured into the river polluting the water. The city's 19th Century "single-system" drainage didn't help either.

It meant water from household kitchens and bathrooms mixed with sewage from the toilets. Normally this flowed through tunnels beneath the streets to the outskirts of Paris where it could be cleaned in water treatment centres.

But, when the rain was too heavy, and there was too much water in the system, some of that waste water drained into the Seine.

In the past 20 years the drainage system has been improved by engineers who built a big underground reservoir to store the excess water during heavy rain.

It means, thankfully, there is less faecal (poo) bacteria floating in the river now.

Would you like to swim in the Seine if you could? Let us know in the comments.