The sources of Lake Toya Onsen and Sobetsu Onsen are closely connected to the activity of Mt. Usu. Their origins as natural springs is clear, which is something rather unusual for hot springs.
With the 1910 (Meiji 43) eruption of Mt. Yosomi, some parts of the neighboring lake rose in temperature to 24℃ as the ground lifted. Toya Onsen is said to have been born after the volcanic activity died down, when gushing hot springs of 42℃ were discovered in the lake waters at the northern foot of Mt. Nishimaru. In 2010, the onsen celebrated its 100-year anniversary by holding various events.
According to the histories of Abutacho, in 1917 (Taisho 6), seven years after the eruption of Mt. Yosomi, Lake Toya Onsen opened for business, as did other onsen accommodations in the area.