THE CALIFORNIA DROUGHT is now in its fifth year, but we still know little about how it has affected public health.

A half-million acres of farmland were fallowed in 2015, leaving thousands of agricultural workers jobless. More than a thousand families saw their drinking water wells go dry. Many more were forced to ration water, either because their well production slowed down, or because a local agency imposed rationing. Many lakes and ponds are experiencing toxic algae blooms, which can lead to sickness in people and pets.