Several of the world’s largest desalination plants sit along the coast of the United Arab Emirates. Every year, they deliver 115 billion gallons of potable water to more than 550,000 people in Dubai alone. But the plants have had to slow or shut down production more frequently over the past decade because of an unexpected disturbance: massive algal blooms in the Gulf of Oman and the Persian Gulf. The algae, known as red tide, clog pipes and filters at the plants. For warning of an approaching bloom, local authorities now consult data from a European Space Agency project, which began in 2012. When a passing satellite captures an image of an algal bloom (and software scans for the algae’s chlorophyll, represented by the intensity of redness), officials alert plant managers, who then have a few days to decide how to adjust water production.