Lake Biwa - A Global Ecoregion
Japan's largest lake, one of the oldest in the world
Snapshot: Ecoregion 185
Size:
670.25 sq. km (262 sq. miles)
Habitat type:
Large Lakes
Geographic Location:
Far eastern Asia: Japan
Conservation Status:
Critical/Endangered
Did you know!
About the Area
Lake Biwa is one of the oldest lakes in the world, estimated to have originated some 4 million years ago. Surrounded by mountains and fed by 460 streams (of which 120 flow directly into the lake), the lake has high species richness and endemism, with 38 snail (19 endemics), 16 bivalve (9 endemics), and more than 50 fish species (12 endemics), in addition to 70 aquatic plants.
The coastal areas of the lake are also important wintering areas for waterfowl, with over 50,000 birds arriving in a typical year. It was designated a Ramsar site in June 1993.
Local Species
Endemic fish species include Biwa trout (Oncorhynchus masou rhodurus), Wataka (Ischikauia steenackeri), Honmoroko (Gnathopogon caerulescens), Biwa higai (Sarcocheilichthys variegatus microoculus), Abura higai (Sarcocheilichthys biwaensis), Sugomoroko (Squalidus chankaensis biwae), Gengorou crucian carp (Carassius cuvieri), Nigoro crucian carp (Carassius carassius grandoculis), Biwako catfish (Silurus biwaensis), Iwatoko catfish (Silurus lithophilus), Isaza (Chaenogobius isaza) and Utsusemi kajika (Cottus reinii).
Endemic mollusks of the genera Heterogen, Semisulcospira, Radix, Gyraulus, Anodonta, Corbicula, and Pisidium are also present in the lake.
Threats
The Lake is the largest in Japan and is relied upon to supply water for 14 million people, as well as industrial and other uses within the watershed. Although the lake is located in a protected area, it suffers from threats associated with invasive species, recreational use, flood-control measures, overfishing, and eutrophication from excessive nutrient inputs.
History
There are several ancient remains in the region, showing that rice was cultivated even in prehistoric times. The paddy surrounding the lake provided an effective spawning ground for local fish and, at the same time, was a place of fishing for farmers. The rice paddy, with showing few negative effects on the lake, has functioned as a part of the lake and a cradle for the sustainable lake-based culture.
The region had a long history of floods caused by the topography and mountain swow melts in spring and heavy rain in rainy and typhoon seasons.
The Seta River, the lake’s only natural draining river, flows from the southern end of the lake to Osaka Bay. After leaving the lake the river runs through a narrow valley for about 20km, where it is further fed with water and mud from its tributaries. The mud, particularly from the Oto river, raised the river bed. This , together with the topography, prevented fast water flow from the lake and flooded the region surrounding the lake with excessive water in the rainy and snow melting seasons. It took several months before the water level returned to normal.
Dredging seemed a solution but the Shogun government rarely allowed it as it meant the urban area downstream would be flooded. Records show that it allowed dredging only 5 times between 1670 and 1831.
The Shogun era was over in 1867 but the region continued to suffer from severe floods. The records show that the floods in 1885 and 1896 were extremely severe, and the Meiji government decided to dredge the river bed and construct a dam to control water flow in Nango, where the Oto river meets the Seta river. Work began in 1902 and was completed in 1905. The dam was 172.71 m long and had 32 3.6m-long gates. It stopped the flooding and was used until 1961 when it replaced by a new dam.
According to the prefecture’s data, the highest water level ever recorded was +3.76 m above the normal level on 13 September 1896 and the lowest was -1.23 m on 15 September 1994.
Resources
• National Geographic
• Lake Biwa Museum
• Lake Biwa Environmental Research Institute
• Kasen
