A dam lake created by damming the Teshio River, the northernmost long river. The Iwaonai Ohashi Bridge, which crosses the lake brimming with water, reflects on the lake's surface, creating a wonderful harmony between natural and man-made structures. In the surrounding area, there are campsites and bungalows, and on the lake, you can enjoy activities such as fishing, canoeing, and boating.

Adjacent to Iwaonai Lake is 'Erica Park.' 'Erica' is a plant of the Ericaceae family, primarily native to Africa and Europe. In this park, 60,000 plants of 11 varieties adapted to this region have been planted, including 'Erica' and its relative 'Calluna.' The lovely, approximately 1-centimeter flowers bloom densely and can be enjoyed from around June to around September.