The mountain yellow-legged frog is found mainly in the waters of Kings Canyon and Yosemite National parks.
But three frogs live at the San Francisco Zoo, protected from the fungus that is killing so many of the amphibians.
Vance Vredenburg is an assistant professor at San Francisco State University; he has spent the past 14 years researching the frogs. He is trying to find out why there has been a 25-30 percent decline in the yellow-legged frog population over the last five years due to a fungus called chytrid.
The fungus is in the water and can penetrate the skin -- terrible because frogs breathe through their skin.
"Their skin can thicken up to 40 times the width that it normally is, so it makes it very hard for them to breathe," Vredenburg said.
Why they get infected is something researchers do not quite yet know.
"The reason the amphibians are so susceptible could be that their immune systems are affected by perhaps pesticide, pollution or global climate change," Vredenburg said.
What he does know is the frogs get re-infected over and over again.
"They don't die until they get very high infection loads, so it's not whether they are infected or not, it's how infected are they," Vredenburg said.
But his study shows that the frogs can survive if we help them keep the infections down at a lower level.
One way, he says, is to treat them in the wild with something as simple as an antifungal agent. That is what saved the lives of the three frogs at the San Francisco Zoo; they too had been infected, and now they show no signs of the chytrid fungus.
Vredenburg's findings are in this week's Proceedings of the National Academy of Sciences.