Lake Onneto is a small lake around 2.5 km that was born from the eruption of Mount Meakan. The name "Onneto," originating from the Ainu language, means "Old Great Swamp." Depending on the season and time of day, a different color is reflected on the surface of the lake, such as clear blue, emerald green, dark blue, and the like, earning it the nickname "Goshikinuma," which means, "Marshes with Five Colors." Particularly on a sunny day, with Mount Meakan and Mount Akan-Fuji in the background, Lake Onneto is a fantastic sight to behold. It is also counted as one of Hokkaido's "Three Major Secret Lakes."