The Okushimako Lake of Gunma prefecture which is known for its blue water was formed through the construction of the Shimagawa Dam in 1999. The lake is one of the top scenic spots of Ibaraki Prefecture, known for the cobalt blue color of its water which is said to be caused by a high Allophane concentration. Because the water is acidic, there are said to be no fish in the lake. However, that doesn't make the scenery any less pretty. The area around the lake has been turned into a park that invites extended walks and photo shooting. Great for nature fans or photographers, visitors to the area shouldn't miss this beautiful spot.