Puno, on the Peruvian side of Lake Titicaca is the largest city on its shores. Recently the Peruvian government has stepped up efforts to reduce contamination from garbage and sewage after the bay became filled with duckweed. As Puno grows so does its effect on the bay. In 2007 its surface was a vivid, electric green that looked more like a broad expanse of grass than water due to uncontrolled growth of duckweed. That plant growth, which resulted from an overabundance of nutrients caused by household sewage run-off, creates a lack of oxygen in the water and chokes off much life below the surface

Photograph: Noah Friedman-Rudovsky