As far as rivers go, there is nothing visibly aquatic about Rio de la Piedad. Translated as The River of Piety, it is just one of 45 waterways in Mexico City that have been paved over and turned into highways and drainage canals. While urban rivers are typically used around the world to irrigate land, preserve biodiversity, and generally improve the environment, in the Mexican capital they are used as sewers, hidden from view under asphalt and encased in metal pipes. And were Rio de la Piedad still exposed to the open air, the smell would likely drive any pedestrian far away.

During the 20th century, Mexico City’s rivers became so polluted that there was a saying: let the river take it. “Everyone threw in all kinds of things,” says urban biologist Delfín Montañana. “That’s why (the rivers) were enclosed in pipes.” This solution went a long way to reliving the sewage problem that had plagued the city, and at the time it made sense to build roads on top of them to increase the city’s traffic capacity. But as the city grew to its current supercity size of around 24 million people and more and more rivers disappeared underground, a new hydrological problem emerged — the concrete umbrella.

An aerial view of some of Mexico City’s covered over rivers.

With no remaining flowing rivers in the city, save one on its Southwestern edge, the abundant rainwater that falls on Mexico City during parts of the year cannot be absorbed by any natural system. In a water-starved city, rain water should be collected in as high volumes as possible so that it could be cheaply or freely distributed to communities that most need it. Instead it falls on a solid plane of concrete and is forced underground into the often overloaded drainage network, resulting in regular flooding across the city. It is a cruel irony that families in Iztapalapa can be so short of clean water that they bathe their babies in bottled water, and at the same time face floods so severe that their homes are submerged in up to five feet of rain.


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