In early June, people in the area of Salem, the capital city of the American state of Oregon, received a warning on their cellphones. City officials sent a message that read: “Civil emergency. Prepare for action.” Within half an hour, the officials sent out a second message. They explained they were not warning of possible violence. The emergency was dangerous bacteria in the city’s drinking water. Microscopic plant-life called algae had suddenly appeared and spread in the local water supply. These so-called algae blooms poison water. Such events are increasing in lakes across the United States. Researchers say the rise in algae blooms is connected to the planet’s rising temperature, or global warming. The researchers say this raises more questions about the effects global warming might have on human health.