The Shono-kawa River runs lazily through Tsuruga. Ikenouchi Marsh, located near its headwaters, is a roughly four-hectare marsh surrounded by mountains. The area, lovingly known by locals as “Awaragaike,” is kept in its natural state, virtually untouched by human hands. Most of the trees in the area are deciduous. The main area is lush with a Japanese alder forest and peat moss, as well as a number of colonies of hygrophytes (plants that grow in moist habitats), with species of plants that can’t be found anywhere else in the prefecture. This marsh is believed to have been formed by the ground sinking due to crustal movement of the Yanagase fault, after which the accumulation of dirt and sand created a natural dam for water, thus keeping the ground wet.