As twilight hits the southern edge of Mexico City, campesinos (peasant farmers) glide through narrow canals between pastures as they make their way over the water to deliver crates of produce. It’s January, the middle of the dry season, and through the slopes of the surrounding hills and volcanoes, desiccated lettuce and spinach fill the fields amid the lagoons of Xochimilco.

San Gregorio Atlapulco, in Mexico City’s Xochimilco municipality, is the last bastion of the once great chinampa economy. …