Lake Biwa

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Lake Biwa is the largest freshwater lake in Japan, located in Shiga Prefecture near Kyoto. It is an ancient lake, at least 4 million years old, and one of the world’s oldest. The lake covers about 670 square kilometers and sits at an elevation of about 85.6 meters. It is about 63 kilometers long and up to 23 kilometers wide, with an average depth of 41 meters and a maximum depth of 104 meters. Water from many rivers flows into it, while its main outlet is the Seta River, which becomes the Uji and eventually joins the Yodo River to reach Osaka Bay.

Lake Biwa provides drinking water for around 15 million people in the Kansai region and serves as a reservoir for Kyoto and Otsu. It also supports local textile industries. The lake is home to a rich ecosystem, with more than a thousand species and subspecies recorded, including many native and endemic fish and molluscs. However, invasive species such as black bass and bluegill have threatened its biodiversity. A famous large-mouth bass caught in 2009 tied the world record.

Historically, the Lake Biwa Canal, built in the 1890s and expanded in the Taishō era, helped revive Kyoto’s industry after the capital moved. The lake has many attractions, including popular beaches on the northwestern shore near Shiga and Omi-Maiko, the Mizunomori Water Botanical Garden, and the Lake Biwa Museum in Kusatsu. The city of Ōtsu sits at the lake’s southern end, and several islands—Chikubu, Takeshima, and the inhabited Okishima—lie in the lake.

Two important archaeological sites near the lake are Awazu Midden, a Jōmon-period shell midden, and Ishiyama-dera, dating to the Early Jōmon period. The area is also known for its environmental protection efforts. Japan’s Eutrophication Control Ordinance, enacted in 1979 and enforced from 1982, set nitrogen and phosphorus limits and banned the sale of phosphorus-containing detergents, a campaign known as Lake Biwa Day. In 1993, Lake Biwa was designated a UNESCO Ramsar Wetland to protect valuable wetlands, and since 1992 there has been a Shiga ordinance to conserve reed beds, which help purify water and provide habitat for wildlife.