Toxic mushrooms spring up in numbers after the first sustained East Bay rains, so park officials issued a wild mushroom warning earlier this month.
Two of the globe's most toxic mushrooms, the Western destroying angel and death cap, grow in the East Bay, but other toxic ones grow here, too.
Symptoms of mushroom poisoning from the Western destroying angel and death cap begin as severe stomach distress and progress to liver and kidney failure if a person doesn't get treatment immediately. It may take half a day for symptoms to appear.
The two mushrooms can kill some animals, too.
East Bay Regional Park District naturalist Trent Pearce documents and teaches about fungi in the Bay Area.
"Both of these mushrooms can be lethal to humans and pets if consumed," Pearce said in a statement. "They are mainly associated with oak trees and can be found growing anywhere oak roots are present."
The Western destroying angel is strictly associated with oak trees while the death cap has been found near other hardwood trees as well.
The death cap is medium to large, and usually has a greenish-gray cap, white gills, a white ring around the stem and a white sac at the bottom of the stem.
The Western destroying angel is also medium to large and usually has a white cap, white gills, a white ring circling the stem that can go away with time and a white sac at its base.
It appears in late winter and in the spring, park officials said. It is not native to California while the death cap is.
"The Park District urges the public to be safe and knowledgeable about toxic mushrooms when encountering them in the parks," said East Bay Regional Park District spokesman Dave Mason, in a statement. "Collecting any mushrooms in East Bay Regional Parks is not allowed."
He added that pet owners are urged to get in touch with a veterinarian right away if they think their pet consumed a toxic mushroom.
Other toxic mushrooms in the East Bay include the Galerina and Lepiota species.