How a Mexican lagoon lost its colors

It’s hard to build a booming tourist economy atop an ecological attraction without destroying it. Some of the colonies of microbes in the lagoon are more than nine thousand years old, but they can survive only as long as the water is pure. Luisa Falcón, a microbial ecologist at the National Autonomous University of Mexico, has studied oligotrophic microbes all over the world. Swimming in the lagoon, she told me, is like going back in time four billion years—“back to the Archean,” she said. “It’s amazing how primitive these sites are.”