Physical Characteristics

Area of the lake: 670.25 km²

Catchment area: 3,174 km²

Volume: Total 27.5 km³

• North basin 27.3 km³
• South Basin 0.2 km³

Maximum depth:

• North basin 104 m
• South Basin 8 m

Mean depth:

• North basin 44 m
• South basin 3.5 m

Length of shoreline: 235 km

Number of inlets: 118 large rivers

Number of natural outlets: one (the Seta River)

Trophic status:

• North basin mesotrophic
• South basin eutrophic

Elevation: 86 m

Climate: Köppen-Geiger climatic zone Cfa - temperate, without dry season, hot summer.

Islands:

• Okishima - 1.51 km²
• Yabase-kihanto (artificial island built in 1980) - 0.75 km²
• Chikubushima - 0.15 km²
• Takeshima - 0.0053 km²

Etymology

Named after the Japanese lute 'biwa' in reference to its shape. Japanese: Biwa-ko. This name dates back about 320 years. Before this time, the lake had various names, including Ohmi no Umi (the Sea of Ohmi). Ohmi is the old name for Shiga Prefecture.

Age

There has been a continuous presence of a lake in the area for approximately one million years, since the formation of Lake Biwa's predecessor, Lake Katata. Lake Katata gradually moved to the west to the present position of the southern basin of Lake Biwa, and then expanded north-east, forming the current north basin about 400 000 years ago.

However, to the south east of Lake Biwa there were four other lakes that existed back to about four million years ago. Due to its age, Lake Biwa is classified as one of the world's few 'ancient' lakes.

Uses

• The lake and its outflowing river system supply 14 million people with drinking water (including the cities of Osaka and Kyoto).
• Commercial fishing, mainly for ayu (Plecoglosus altivelis altivelis) in recent years.
• Recreation, especially sport fishing and boating.

Conservation Status

• Lake Biwa was designated a quasi-national park in 1950.
• The entire Lake Biwa region was designated as a wildlife sanctuary in 1971.
• Lake Biwa was registered with the Ramsar Convention on Wetlands in 1993 as a wetland of international importance.

The Lake's Fauna and Flora

More than 3100 species have been recorded from Lake Biwa and vicinity, and of these, over 2300 species are aquatic or semiaquatic.

* The Japanese otter, which became extinct in the Lake Biwa region in the 1910s, and extinct from all of Japan by 1979.

Endemic Species

Some species have been reported only from Lake Biwa. 62 of these species are endemic to the lake, i.e. live nowhere else. Another 84 are suspected to be endemic as they haven't been found anywhere else yet, but further research is required to confirm this.

Some of the endemic species are listed below.

Fish
'Honmoroko', a minnow (Gnathopogon caerulescens). Habitat is deep open water. This fish is prized for its taste when grilled.
'Gengorobuna', Japanese crucian carp (Carassius cuvieri). Habitat is middle to surface waters. The Japanese name of this fish relates to a famous local legend.
'Biwamasu', Biwa Salmon (Oncorhynchus sp.). Habitat is cool middle waters. Prized for its lean, tasty flesh.
'Isaza', a goby (Gymnogobius isaza). It spends the daytime at depths of 30m or more, coming to the surface at night.
'Biwako-ohnamazu', Lake Biwa Catfish (Silurus biwaensis). Habitat is the bottom of the lake. This is the largest fish in the lake.
'Biwahigai', Biwa oily gudgeon (Sarcocheilichthys variegatus microoculus). Habitat is sand and gravel. This species lays its eggs in clams.
'Nigorobuna', a crucian carp (Carassius buergeri grandoculis). Habitat is fairly deep water. The juvenile fish grow in reed beds. It is used for 'funazushi', a local dish of fermented fish.
'Wataka', a carp (Ischikauia steenackeri). Habitat is middle to surface waters. It eats plants and in Japanese is also known as the 'horse fish'.
'Utsusemikajika', a sculpin (Cottus reinii). This species is found in Lake Biwa and the surrounding rives of the drainage basin.
'Biwayoshinobori', a goby (Rhinogobius sp.). This endemic species was first reported in 1998. It lives in the open waters of the lake, coming closer to shore during the summer to lay eggs.
'Sugomoroko', a minnow (Squalidus chankaensis biwae). Until recently, this species was considered to be the same as a species found in other parts of Japan, but research has determined that the Lake Biwa specimens are a separate subspecies.
'Aburahigai', a minnow (Sarcocheilichthys biwaensis). Habitat is rocky areas of the lake, but recently its numbers have dramatically decreased.
'Biwakogata Sujishimadojou', a loach (Cobitis minamorii oumiensis). Habitat is the lakeshore areas and rivers of the Lake Biwa region, but recently numbers have dramatically decreased.
'Ohgata Sujishimadojou', a loach (Cobitis magnostriata). Habitat is the lakeshore areas and rivers of the Lake Biwa region, but recently numbers have dramatically decreased.
'Iwatoko-namazu', Biwa rock catfish (Silurus lithophilus). Inhabits the rocky areas of the north of the lake. Of the three species of catfish living in Lake Biwa, this one is said to be the most tasty.
Molluscs
'Biwakomizushitadami', a gastropod (Biwakovalvata biwaensis). Lives at depths ranging from 2 to 80m on muddy sediments, but can also be found on gravel in the north basin. The diameter of the shell is 3 to 5mm.
'Nagatanishi', a gastropod (Heterogen longispira). Lives at depths ranging from 2 to 30m. It has become rare in the south basin. It is a large species, with a shell reaching 70mm in length.
'Ikechougai', Biwa pearly mussel (Hyriopsis schlegeli). Habitat is sandy mud at depths of 1 to 5m. This species reaches 255mm across. It played an important role in the freshwater pearl industry.
'Setashijimi', the Seta clam (Corbicula sandai). Can be found throughout the lake at depths of 2 to 30m. Size ranges from 20 to 35mm. It is eaten by local people.
Water plants
'Nejiremo', a water plant (Vallisneria asiatica var. biwaensis). The leaves have a characteristic twist along their length.
'Sannenmo', a water plant (Potamogeton biwaensis). The leaves don't have a stalk, and are linear with a pointed tip.
Plankton
'Biwakunshoumo', an algae (Pediastrum biwae). In Japanese this species is called 'the decoration' due to its shape.
'Biwatsubokamuri', an Amoebozoa (Difflugia biwae). By swallowing sand grains this amoeba produces a hard shell.

Alien and invasive species

234 species are alien to the Lake Biwa region. Many of these are plants along the shores, but also many unwanted pets have been released into the lake.

Some alien species have established populations in the lake and have become invasive. Some of the most common invasive species living in the lake include the following:

Invasive Species
Black bass (Micropterus salmoides). From North America, illegally released into the lake during the 1970s for sport fishing.
Blue gill (Lepomis macrochirus). A gift to the Crown Prince of Japan from Chicago, this species was bred and then released in many parts of Japan, including Lake Biwa.
Red-eared slider (Trachemys scripta elegans). From North America, unwanted pets released nationwide.
Red swamp crayfish (Procambarus clarkii). From North America, imported for aquaculture and the pet trade.

Data from: Lake Biwa: Interactions between nature and people. Second edition. Kawanabe, H., Nishino, M. & Maehata, M (Eds), 2020, Springer, 932 pp, ISBN 978-3-030-16969-5.