Which ancient freshwater lake is Japan's largest lake?

Lake Biwa is Japan’s largest lake and an ancient freshwater lake.

Located entirely in Shiga Prefecture on Honshu, northeast of Kyoto, Lake Biwa covers about 670 square kilometres. It is a tectonic lake that has existed for at least four million years, making it one of the world’s oldest surviving lakes. Its long history has allowed an unusually rich freshwater ecosystem to develop.

More than 1,000 species and subspecies have been recorded in the lake, including numerous endemic fish. Lake Biwa has 46 native fish species and subspecies, with several found nowhere else or almost nowhere else. It also supports wetlands and attracts thousands of waterbirds each year.

The lake is central to the region’s history and economy. Its outlet, the Seta River, becomes part of the Yodo River system and eventually reaches Osaka Bay. The Lake Biwa Canal helped revive Kyoto’s industry after the imperial capital moved to Tokyo, while the lake continues to supply drinking water to roughly 15 million people in the Kansai region.

Lake Kasumigaura is Japan’s second-largest lake, a common source of confusion in comparisons.