At first the biologists noticed something unusual about the dead fish washing up on the shore of the Salton Sea: All of them were fully grown, at least 7 inches long. There were no smaller fish among the carcasses pushed ashore by the lapping waves.

Then the biologists started seeing other clues in the birds. Western grebes, which normally arrive by the thousands to forage, were nowhere to be found. Thousands of Caspian terns would normally stop off to nest, but they were also missing.