Lake Kussharo (quot;Kussharo-koquot; in Japanese) is a freshwater caldera lake located about 10 km west of a href="http://www.travel-around-japan.com/k11-54-lake-mashu.html"; target="_blank"Lake Mashu/a. It is one of the the biggest caldera floors in Japan, and is about 12 km long and 6 km across and 117 meters deep. An island, which is a volcano, is in the center of the lake.