Ōtsu is the capital city of Shiga Prefecture, Japan. Ōtsu is known as the main port of Lake Biwa, the largest lake in Japan. It briefly served as the capital of Japan from 667 to 672 AD during the Asuka period (538 – 710). The city is home to numerous sites of historical importance, notably the temples of Mii-dera, Ishiyama-dera, and Enryaku-ji and the Hiyoshi Taisha shrine. Enryaku-ji is part of the UNESCO World Heritage Site "Historic Monuments of Ancient Kyoto (Kyoto, Uji and Otsu Cities)". Ōtsu was incorporated as a city on October 1, 1898.
As of October 1, 2016, the city has an estimated population of 341,314 and a population density of 730 persons per km2. The total area is 464.51 km2 (179 sq mi).