Lake Shumarinai is a dammed lake created by the construction of the Uryu Dam, and is the largest man-made lake in Japan, with a surface area equivalent to about 30 Tokyo Disney Lands. The lake still retains its original natural state.

The lake, with its 13 islands of various sizes, changes with the seasons. The intricate topography, reminiscent of the fjords of Northern Europe, nurtures lake life and deep virgin forests, and the lake, surrounded by deep nature, is called a mysterious lake that is home to Japan's largest freshwater fish, the Itou, which is known as a phantom fish. During the trout season, the lake attracts anglers from inside and outside of the province, and sometimes even from overseas, and in winter it is crowded with people fishing for wakasagi (smelt).

During the summer camping season, the lake attracts many campers. The fact that the area is almost entirely untouched by tourism makes it popular with well-traveled campers and riders, and one of its features is that many repeat visitors come back to the area as a place where they can spend their time in a relaxed and leisurely manner.