The Salton Sea is a disaster in slow motion. For more than a century, California’s largest lake has been sustained by Colorado River water, which irrigates Imperial Valley farms and drains into the lake. But the Salton Sea will start shrinking rapidly at the end of this year, when increasing amounts of river water will be diverted from farms to cities. As the lake’s shorelines retreat, thousands of tons of lung-damaging dust are expected to blow from the exposed lakebed, polluting the Imperial Valley’s already-dirty air.