Lake Nojiri, Natural lake in Shinano, Nagano Prefecture, Japan

Lake Nojiri is a natural lake on a 654 m plateau between Mount Madarao and Mount Kurohime in Shinano, Nagano Prefecture. It covers 4.56 km², reaches 39.1 m deep, and drains through the Ikejiri River to the Sea of Japan. Its irregular shoreline has a narrow western arm and a rounded northern inlet.

The water body formed through volcanic activity and natural damming processes in the mountains long ago. Later it became the site of an early hydroelectric facility that advanced Japan's development in this technology.

The name Nojiri derives from Shinano-jiri-ko, and an alternative name, Fuyō-ko, comes from the lake's shape. On the western shore, the Kamiyama International Village has been run by the Nojiri Lake Association since 1921 and is counted among Japan's three great foreign summer resorts. Boats reach Biwa Island, which holds Uga Shrine and a tomb attributed to the warlord Usami Sadamitsu.

The lake sits at 654 m between Mount Madarao and Mount Kurohime; reach it by bus from Kurohime Station on the Shinano Railway or from Iiyama Station on the Hokuriku Shinkansen, getting off at Nojiri-ko. The lake rarely freezes in winter, so smelt fishing continues from stove-heated dome boats. Sightseeing boats run to Biwa Island, where Uga Shrine and a tomb attributed to Usami Sadamitsu stand.

In 1946 a tusk of Naumann's elephant, an extinct species named after geologist Heinrich Edmund Naumann, was found by chance; excavations from 1962 at the Tategahana promontory on the western shore yielded stone and bone tools plus deer fossils, dated to about 40,000 years ago and read as a kill-butchering site.