[1] In dozens of cities around the world, a quiet revolution is flowing through the streets. From Seoul to Sheffield, from Zurich to Singapore, engineers and residents are tearing up concrete to uncover rivers that were buried generations ago. The movement, known as ‘daylighting’, has already reached more than 70 cities, and its global popularity shows no sign of fading. In Seoul, a six-lane motorway was peeled back to reveal a stream that now draws millions of visitors a year; in smaller towns, a single modest brook is enough to transform a forgotten back street. People who once crossed a dull grey road without a second thought now pause on a bridge to watch clear water slip past, and children lean over the railings to count the fish below. What began as the eccentric idea of a handful of campaigners has become, in barely two decades, a mainstream ambition for city planners on almost every continent.

[2] For much of the twentieth century, urban rivers were treated as a nuisance rather than a treasure. As towns expanded and traffic multiplied, streams were seen as obstacles to traffic and as convenient drains for waste. Factories tipped their refuse into them, and on a hot day the smell could be unbearable. The simplest solution, it seemed, was to bury them: the water was forced into underground pipes, and a road or car park was laid neatly on top. For the engineers of the time it felt like progress, a tidy victory of concrete over mud. Hidden away in these dark tunnels, the rivers were quickly forgotten, vanishing even from the city’s maps, and the fish, insects and birds that had depended on them vanished with them.

[3] Daylighting reverses this process, undoing in a few months the work of half a century. Workers break open the covering, haul away the rubble, reshape the banks with soil and native plants, and let the river breathe again. The effects can be remarkable, and they arrive far faster than anyone expects. Within months, fish and insects return, and birds soon follow them; herons and kingfishers have been spotted hunting in city centres that had not seen them in living memory. On hot afternoons the open water cools the surrounding air by several degrees, offering welcome relief in cities where summers grow fiercer each year. A street that was once a heat trap of baking tarmac becomes a place where people are glad to linger.

[4] The benefits are not only ecological. A restored river gives people a green ribbon to walk beside, a place to meet neighbours, push a pram, or simply escape the noise and fumes of the traffic. Small shops, restaurants and cafes often open along the new banks, drawn by the crowds the water attracts, and the value of nearby homes tends to rise accordingly. Schools bring children to study the wildlife, while joggers and cyclists trace the river’s course at dawn. A feature that a town was once ashamed of — something to be paved over and hidden — becomes, almost overnight, a source of genuine local pride.

[5] Yet bringing a river back to the surface is rarely easy or cheap. The work is expensive, often running into many millions, and in crowded districts there may be little room to widen the channel between existing buildings. Some residents worry that an open river could flood their homes after heavy rain, remembering the very dangers that led people to bury it in the first place. Local businesses, meanwhile, fear the disruption of months of noisy construction, with roads closed and customers kept away. Planners must answer all of these concerns patiently, and win the trust of the community, before a single slab of concrete is lifted.

[6] And there is a deeper lesson hidden beneath the pavement. We tend to imagine a city as something separate from nature, a place of stone and steel and glass where rivers and wild creatures have no real part to play. The daylighting movement quietly suggests the opposite. All those years, beneath the traffic and the shopping streets, the water had gone on flowing in the dark, patient and unseen. It was never truly gone; it was simply waiting, out of sight, for us to remember it — and to find the courage to let it back into the light.