The area around Lake Onuma has been protected as a Hokkaido Prefectural Park since 1903 (Meiji 36), and park facilities have been developed, making it one of the oldest natural parks in the country. On April 17, 1915 (Taisho 4), it was selected as one of the New Three Views of Japan, along with Miho no Matsubara (Shizuoka Prefecture) and Yabakei (Oita Prefecture). In 1957 (Showa 32), with the backing of various campaigns to elevate Lake Onuma to a quasi-national park, a petition was submitted to the Hokkaido Prefectural Government. In July of the following year (1958), Lake Onuma became the 13th quasi-national park, and Lake Onuma and Mt. Komagatake became special national protected areas.

There are 126 islands of various sizes floating on Lake Onuma and the other three lakes, adding a delicate touch of color to the landscape of Lake Onuma. Some of these islands are connected by arched bridges, and you can enjoy island hopping on foot from the park plaza. In the lake's inlet surrounded by islands, you're sure to spot aquatic plants such as water lilies, and carp and crucian carp jumping up and down, their leaves swaying. If you're lucky, you might even see kingfishers darting across the water, or squirrels busily munching on nuts.

In autumn, the lakeside areas of Lake Onuma, Lake Konuma, and Junsai Numa Swamp take on vibrant colors at Onuma Quasi-National Park. The vibrant crimson lakes and the distinct ridgeline of Mount Komagatake vividly showcase the beauty of nature. There are various ways to view the autumn leaves, such as cycling along the circular road, heading out on the lake by canoe or boat, or climbing Mount Higurashi (303m above sea level), located to the west of the park and offering views of the entire lakeside area. Each offers a different view to enjoy.

You can go smelt fishing during the winter. You can do it from the pier in December before the lake freezes over, and on the ice from early January to mid-March. There are many facilities where you can go empty-handed and enjoy the experience, so be sure to give it a try. *Some facilities will fry the smelt you catch for an additional fee.