A blue American Bullfrog (Lithobates catesbeianus) was photographed by Jim Wiegand on the shore of Shasta Lake. The coloration is caused the absence of yellow pigments in their skin. This condition is rare, only about 1 in a million have it.
The American Bullfrog is actually an invasive species in California. With their size and appetite, they devour smaller native frog species and they are spreading diseases. They were imported into California for pet trade, food, and dissections. The frogs escaped or people let them go and now they are almost everywhere.