Lake Hamana (Hamanako) in Shizuoka Prefecture is Japan's tenth largest lake (by area). It spans the boundaries of the cities of Hamamatsu and Kosai. The lake has an area of 65.0 km² and holds 0.35 km³ of water. Its circumference is 114 km. At its deepest point, the water is 16.6 m deep. The surface is at sea level. Lake Hamana is a commercial source of cultivated Japanese eel, nori, oysters and Chinese soft-shelled turtles.
Fishers take sea bass,[disambiguation needed ] whiting, and flounder, among others. The lake has been developed as a resort area, with boating as a feature. In ancient times, Lake Hamana was a fresh-water lake. However, a great earthquake in 1498 altered the topography of the area. As a result, the water in the lake is now brackish.