Three normally white polar bears at Higashiyama Zoo and Botanical Gardens in central Japan changed their color in July after swimming in an algae filled pond.
A zoo official say the sight seems to shock visitors and has prompted many questions about whether the animals are sick or carrying mold.
He says high temperatures in July and August and less-frequent water changes because of the zoo's conservation efforts caused the algae growth in the bears' pond and safety moat. The official says once the algae enters hollow spaces in the bears' fur, it's hard to rinse off.
The bears are expected to return to their natural color when the algae growth subsides in November.