A colossal water basin must make the dirty Seine ready for swimming for the Summer Games

• Frank Renout

  France correspondent

This summer, the Seine in Paris will host the Olympic open water swimming and triathlon competitions. One problem: the water quality is not yet good enough. Various plans should ensure that this is the case when the Summer Games start at the end of July.

In recent years, a colossal water basin with a capacity of 50,000 cubic meters of water, the size of about twenty Olympic swimming pools, has been built in the east of Paris. This basin must ensure that it is safe to swim in the Seine during the Olympic Games. Today it was officially inaugurated.

The basin is an underground round concrete tank, with a diameter of 50 meters and a depth of 30 meters. In case of heavy rainfall, the rainwater is intended to be stored in it.

So far, heavy rain has caused major problems in Paris. The sewers in Paris are becoming overflowing and overflowing. To prevent dirty sewage, including human feces, from ending up on the streets, it is discharged into the Seine.

This means that all kinds of harmful substances end up in the river during bad weather, including E. Coli bacteria. It is found in human feces and can cause symptoms such as nausea, vomiting and diarrhea. Partly for this reason, it has been forbidden to swim in the Seine in Paris for 100 years.

During the Olympic Games this summer, swimming competitions will be held in the Seine for the first time. These can only continue if the water is clean enough. An action plan was put into action as early as 2016. With a budget of 1.4 billion euros, the Seine had to become bacteria-free again.

The underground basin costs 90 million euros and is one of the showpieces of the Paris municipality. A special 600-meter tunnel was even dug under the city to channel rainwater to the basin.

However, this project is not a complete solution for cleaning the river: in the event of very heavy rainfall, the concrete basin is not large enough, the authorities warn.

That’s why more has been done. Water treatment stations east of Paris are equipped with ultraviolet filters. They must remove various bacteria from the water before it reaches Paris. A completely new water treatment plant was also completed on the east side this month, which will clean 700 liters of water per second.

Furthermore, sewer connections of houses have been checked and improved and houseboats in Paris are no longer allowed to discharge waste water into the Seine.

According to environmental organization Surfrider, it is not enough. The water quality is said to be “alarmingly poor”. The organization took a water sample 14 times in the past six months. Only once did the quality meet the standards for bathing water as set by the European Union. The standards were exceeded the 13 other times.

“There are therefore risks for the athletes,” said a Surfrider spokesperson. “The pollution can lead to moderate health problems such as stomach flu, but also to serious illnesses such as an infection with the Staphylococcus Aureus bacteria.”

The authorities point out that not all work has yet been completed and that water quality is generally better in summer, i.e. during the Olympic Games, than in winter. “The quality will be fine when the Games start,” the prefecture said. “Thanks to all the work, the water in the Seine will be of good quality by the summer,” said councilor Pierre Rabadan.

And what if it all turns out to be insufficient? “Then we will simply postpone the matches for a few days,” the local authorities said. Because water quality can change from one day to the next and still meet the standards.