Tests showed the bird had 10 times the safe amount of lead in its bloodstream after it was caught at the Bitter Creek National Wildlife Refuge last month, according to Audubon California, an environmental and conservation group.
Only about 300 California condors remain in the world.
"Lead poisoning is a tremendous threat to these remarkable birds," said Glenn Olson, executive director of Audubon California.
Researchers believe the condor, North America's largest flying bird, may have ingested lead paint or soil contaminated with lead bullet fragments.
Scientists at the zoo were not able to determine the source of the bird's lead poisoning, said Dr. Janna Wynne, a veterinarian with the Los Angeles Zoo.
The California Fish and Game Commission is set later this month to consider a ban on lead ammunition for hunting in condor habitat.