This is a dammed lake dammed by the Teshio River, the northernmost and longest river in Japan. The Iwaonai Bridge, which crosses the lake filled with water, reflects on the surface of the lake, and a wonderful harmony of natural and man-made formations can be seen.

Erika Park" is located adjacent to Lake Iwaonai. Erika" is a member of the azalea family that is mainly native to Africa and Europe. The park is home to 60,000 plants of 11 species adapted to the area, including "Erica" and its companion "Caruna." The pretty flowers, about 1 cm in diameter, bloom in dense clusters and can be admired from around June to September.