Unearthing Paris’ Mythical Second River | Hope is Real

Why this story matters: Data-driven progress often moves at a pace that is too slow for breaking news, but its impact is far more permanent. This story takes a closer look at a long-term success that is finally reaching a major, positive milestone.

Quick summary: This story highlights recent developments related to climate environment, showing how constructive action can lead to meaningful results.

Only knee-deep in parts yet relatively wide, the Bièvre gently flows with transparent waters that shimmer in the afternoon sun.

A shoal of fish lazily linger beside a large stone in one section. Further along, birds and butterflies weave between the long grasses lining the banks. From here, the waterway continues 10 kilometers north all the way to the Seine, Paris’ iconic river.

But for over a century, the Bièvre, the city’s mythical second river, was not visible.

“This was once completely covered over,” says Marie Bontemps, strolling beside a stretch of water in the Parisian suburb of Haÿ-les-Roses amid a record-breaking, deadly June heatwave in the French capital. “But we’re liberating the Bièvre.”

In Paris, much of the Bièvre — a tributary that runs 36 kilometers from its source in Guyancourt in the Yvelines department to where it meets the Seine itself — is still hidden, mostly masked by concrete several meters underground. But as city authorities and neighboring municipalities contend with increasingly extreme heat and flood risks, paired with the desire to bring back biodiversity and increase green space for urban residents, they are unearthing this ancient waterway.

“The revival of the Bièvre is a deeply eco-friendly project to cool the city and adapt it to climate change,” declared Dan Lert, deputy mayor of Paris in charge of ecological transition, the climate plan, water and energy, in a public announcement last year.

For many centuries, the Bièvre served an important role for communities living in proximity. According to Raphaël Morera, an expert on the Bièvre and co-director of the National Centre for Historical Research (CNHR), marshy areas of the basin were drained and cultivated during the Middle Ages, including by monks in Paris who diverted the river to water their gardens.

But as the Industrial Revolution arrived, exploitation accelerated. Tanneries, dyers and laundries — profiting from the fact the waters were free of limestone, allowing it to be used in a diverse number of ways — sprouted up on the edges of the river.

“It was seriously important for the Parisian economy,” says Morera.

The Bièvre, which some claim takes its name from the beavers that once inhabited it (beber in Celtic), went on to earn something of a mythical reputation over the years. It was documented by pioneer photographer Eugène Atget, described in the Renaissance poetry of François Rabelais and even featured in Victor Hugo’s Les Misérables.

But the local industries used and abused the Bièvre’s waters, effectively turning it into an open-air sewer. Due to public health concerns, Parisian authorities decided to completely bury it in concrete by 1912 and integrated the Bièvre into the Paris sewer system. Outside of the city center, the remainder of the river was closed off by 1935.

“We made it disappear, like it was the river’s fault,” adds Morera.

Yet in the 1980s, the currents of opinion began to shift. Local campaign groups argued that the Bièvre should be freed from the concrete. Then the idea started to gain traction among public authorities, leading to a 2006 national law establishing river restoration as a priority, which itself built on the 2000 EU Water Framework Directive.

Globally, momentum to restore and protect rivers, which are increasingly degraded, is growing. The World Wildlife Fund’s Freshwater Challenge, launched in 2023, aims to restore 300,000 kilometers of rivers and 350 million hectares of wetlands by 2030. Proponents like the WWF say that healthy rivers reduce urban temperatures through evaporative cooling, soak up heavy rains to reduce the likelihood of floods and provide vital ecological habitats.

And Paris, which has seen a spike in biodiversity in the Seine following a long-term management program, is among many cities, including Seoul and Madrid, that are going with the flow of river restoration.

Today, the return of the Bièvre is well underway. Nearly four kilometers of the river have been restored or reopened to date, leading to it regaining its status as a watercourse.

In some sections, pipeline has been removed and the riverbed excavated to let the water flow in the open air once again. In Haÿ-les-Roses, the riverbanks have been landscaped and planted with vegetation to provide natural habitats. In Arcueil and Gentilly, restoration has included the creation of a flood retention area where water quality is being regularly monitored. Meanwhile in Paris city center, hundreds of meters of the river are set to open in the southeastern Kellermann Park by 2028.

Bontemps, a project manager for the Joint Syndicate of the Bièvre Watershed (SMBVB), a public body responsible for managing the river, has been working with city authorities, farmers, businesses and residents to establish more sustainable management of the water and natural ecosystems.

Many homes in Haÿ-les-Roses have toilet systems that dump wastewater directly into the Bièvre, for example, so Bontemps has worked with authorities to reduce bureaucracy for residents who want to renovate piping, channeling waste instead into treatment facilities. She has also helped install signage and improve awareness for companies who continue to inadvertently dump wastewater in the drainpipes beside the river.

“They think it’s going into water treatment facilities, but it flows into the Bièvre,” she explains.

Those efforts are helping to clean up the water. Between 2020 and 2024, the amount of wastewater going into the Bièvre fell by the equivalent of the amount produced by roughly 2,400 people each day, according to SMBVB estimates. The target is an overall reduction of 4,374 BOD5 people equivalent, the water pollution indicator, by 2030. The result is that the waters of the Bièvre now no longer need to be treated in a purification facility.

In more rural areas, the Inter-municipal Authority for Sanitation in the Bièvre Valley (SIAVB), which is responsible for a stretch of 18 kilometers of the river outside the capital, has been working to create a system of sustainable river management. That includes flood control, water quality improvement and reduction of the use of pesticides in the catchment area. It has also rerouted parts of the river, adding more curvature to support biodiversity.

“We have seen the water quality improve,” says Hervé Cardinal, director of technical services for the SIAVB.

“But it also has value in its beauty, it provides green space and acts as a cooling hub.”

Cardinal adds that progress has been greatly aided by the commitment of sustained financial investment. In December 2025, a further €68.6 million ($78 million) was allocated by the Seine-Normandie Water Agency to continue the restoration between 2026 and 2030, adding to the €76 million dispersed between 2020 and 2024.

“Before, it was more complicated to get funding,” says Cardinal.

The reality, however, is that the Bièvre will never be entirely uncovered. Restoring a river in an urban environment can require an enormous amount of digging and sometimes cutting down trees. In parts of Paris, the river is 10 or 15 meters under the surface, sitting below houses and metro tracks, among other immovable objects.

The idea is rather that the Bièvre will be exposed to the sky in select sections of its course in the city where there will be pedestrian and cycle paths. In Paris city center, the Bièvre is set to reappear in René-Le Gall Square and the Jardin des Plantes botanical garden as well as Kellermann Park.

By increasing Parisians’ daily interactions with rivers, these glimpses of the restored Bièvre could help change mentalities and relationships with nature, setting the city on a more sustainable course long into the future.

“In Paris, the evocations of the river, even if they are only little parts, can give a sense to urban life, to remind us of the past and the place of water in the city,” says Morera.

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