Okama, Volcanic crater lake in Mount Zao, Japan.
Okama is a circular crater lake at the summit of Mount Zao in Miyagi Prefecture, Japan, formed by a volcanic eruption. The lake measures roughly 360 meters (1180 feet) across, reaches a depth of about 60 meters (197 feet), and sits at an elevation of around 1550 meters (5085 feet) above sea level in a barren landscape of volcanic ash and rock.
The crater lake formed during the 1720s when an eruption in the Zao Mountains volcanic complex reshaped the summit. Since then, the volcano has erupted multiple times, with the most notable activity occurring in the 18th and 19th centuries and minor events continuing into the 20th century.
Local people call the crater Goshikinuma, which means Lake of Five Colors, because the water changes hue depending on weather conditions. On sunny days the surface glows turquoise green, while fog or rain brings out gray and blue tones that make the water look like liquid metal.
The viewpoint is accessible via the Zao Echo Line road, which opens from late April to early November when snow does not block the route. Visitors can take a chair lift from the lower parking area or walk the short trail up to the crater rim, where the view over the water is unobstructed.
The extremely acidic water allows only a few microscopic organisms such as the rotifer Rotaria rotatoria and certain diatom species of the genus Pinnularia to survive. These tiny life forms have adapted so completely to the harsh conditions that they could not exist in normal freshwater environments.
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