|Primary outflows||Pacific Ocean|
|Surface area||65.0 km2 (25.1 sq mi)|
|Average depth||4.8 m (16 ft)|
|Max. depth||16.6 m (54 ft)|
|Water volume||0.35 km3 (280,000 acre?ft)|
|Shore length1||114 km (71 mi)|
|Surface elevation||0 m (0 ft)|
|1 Shore length is not a well-defined measure.|
Lake Hamana (, Hamana-ko) is a brackish lagoon in Shizuoka Prefecture, Japan. Formerly a true lake, it is now connected to the Pacific Ocean by a channel. As an internal body of water, it is considered 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, 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 freshwater lake. However, a great earthquake in 1498 altered the topography of the area and connected the lake to the ocean. As a result, the water in the lake is now brackish.
The old name for this lake is Tohotsu-afumi (?), which means "distant fresh-water lake" and later changed phonologically to T?t?mi (). From the perspective of the capital in the Kinai, T?t?mi is more distant than the other famous lake, Chikatsu-afumi or ?mi (now Lake Biwa), the "nearby fresh-water lake." The name T?t?mi was also used for a former province in which the lake is located (T?t?mi Province).
At the end of World War II two experimental Type 4 Chi-To tanks were dumped into the lake to avoid capture by Occupation forces. One was recovered by the US Army, but the other was left in the lake. In 2013, there were efforts to locate the remaining tank, but it wasn't found.