Thousands of water birds that died mysteriously at the Salton Sea National Wildlife Refuge seem to have been poisoned by a toxic form of algae that blooms in the huge, salty lake, according to new findings by the U.S. Fish and Wildlife Service.
Clark Bloom -- manager of the federal refuge in farm-rich Imperial County, Calif., near the U.S.-Mexico border -- said the discovery, although preliminary, is a great relief because the bird deaths have perplexed and worried wildlife biologists since they began three years ago.
"It was extremely frustrating to go through this," Mr. Bloom said. "The only thing we did know is that we were picking up a lot of bodies."
About 15,000 eared grebes wintering at the Salton Sea died in February and March of 1992 and another 20,000 died during the same period in 1994. Federal biologists had been stumped after ruling out common infectious diseases and chemical pollutants. Tests on the carcasses of grebes detected high concentrations of a poison, called microcystin, in their livers. Microcystin, produced by blue-green algae, has no known antidote.
In some birds, the toxin was "high enough to account for acute lethal liver toxicosis," according to a report by Wayne Carmichael, an aquatic biologist at Wright State University in Ohio.
The Salton Sea is a major wintering ground for migratory birds including eared grebes, which have red eyes and golden ear tufts.