Houtan Park in Shanghai cleans river water

A manmade stream that draws from Shanghai’s Huangpu River takes in water so polluted it shouldn’t be touched. The stream slows the water, aerates it, and filters it through vegetation, until it emerges clean enough that people can swim in it. The project, called Houtan Park, runs a mile along the riverbank through what was once an urban brownfield, a former industrial site and scar on the urban landscape that is similar to many others in cities around the world. The park, toured by Harvard President Drew