Mount Zao (蔵王山, Zaō-san) is a volcano that consists of a cluster of strato-volcanoes on the border between Yamagata Prefecture and Miyagi Prefecture in Japan.
The most active volcano in northern Honshū, the central volcano of the group includes several lava domes and a tuff cone, Goshiki-dake, which contains a crater lake named Okama.
Also known as the 'Five Color Pond' (五色沼, goshiki numa) Okama changes colour depending on the weather. The lake lies in a crater formed by a volcanic eruption from the 1720s. The lake is 360 metres (1,200 ft) in diameter and 60 m (200 ft) deep, and is one of the main tourist attractions in the area.
The appearance of the Five Colour Pond was based on real-life images of the location.