Lake Biwa

▶Japan’s largest lake
Lake Biwa has an area of about 670 km². Its shoreline stretches approximately 235 km, though it is about 200 km if you follow the roads, and you can complete one lap by bicycle in roughly two days and one night. The deepest point of Lake Biwa is about 104 m. It is about 60 km from north to south and about 20 km at its widest point from east to west.

The lake holds about 27.5 billion tons of water. This is equivalent to about 11 years’ worth of water used by the 14.5 million people in the Yodo River basin who rely on Lake Biwa’s water.

▶A precious “ancient lake” found in only about 20 places in the world
Lake Biwa is one of the world’s oldest lakes. About 4 million years ago, a shallow, narrow lake formed near what is now Iga City in Mie Prefecture (Oyamada Lake). Since then, it has changed shape and moved to its present location, influenced by fault movement that caused the ground to sink and by sediment filling in the basin. The present Lake Biwa has remained in this location for at least about 400,000 years.

Most lakes disappear in about 10,000 years due to sediment accumulation, but lakes with a history of more than 100,000 years, like Lake Biwa, are rare. In the world, there are only about 20 lakes with a history of over 100,000 years and endemic species (ancient lakes), and in Japan, Lake Biwa is the only one.

▶A “treasure house” of living creatures
Over the very long span of about 4 million years since the first ancient Lake Biwa, and even over the roughly 400,000 years since it became the present Lake Biwa, some of the organisms in the lake have evolved independently, giving rise to species found only in Lake Biwa (endemic species). More than 1,700 species of aquatic plants and animals have been reported in Lake Biwa, and more than 60 of them are endemic to the lake.

▶A lake where you can swim and play
At Lake Biwa, lake sports such as yachting and canoeing are popular, and about 700,000 people visit its beaches and marinas each year. The shoreline has many flat roads, and on “Biwakoichi,” the cycling or walking route that goes around Lake Biwa, you can experience the lake’s immense scale firsthand.