Only knee-deep in parts yet relatively wide, the Bièvre gently flows with transparent waters that shimmer in the afternoon sun. Unearthing the Bièvre, Paris' second river, has been a long time coming.

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. Now, unearthing the Bièvre is underway.

“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, demonstrating the importance of unearthing the Bièvre. 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.

Read the full article about unearthing the Bièvre in Paris by Peter Yeung at Reasons to Be Cheerful.