Lake Biwa Facts

Volume: Total 27.5 cubic km.

• North basin 27.3 cubic km.
• South Basin 0.2 cubic km.

• North basin 104m.
• South Basin 8m

• North basin 44m.
• South basin 3.5m.

Catchment area: 3174 square km.

No. of inlets: approx. 340.

No. of natural outlets: one (the Seta River).

Trophic status:

• North basin mesotrophic.
• South basin eutrophic.

However, to the south east of Lake Biwa there were four other lakes that existed back to about 3.5 million years ago. Due to its age, Lake Biwa is classified as one of the world's few 'ancient' lakes.

Uses:

• Supplies 14 million people with drinking water (including the cities of Osaka and Kyoto).
• Commercial fishing, mainly for ayu (Plecoglosus altivelis altivelis) (right) in recent years.
• Recreation, especially sport fishing and boating.

• 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.

No. of endemic species/subspecies: 59, including:

• 11 species/subspecies of fish (19% of total)
• 9 species of bivalves (56% of total)
• 11 species of gastropods (39% of total)
• 12 species of insects (7% of total)

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 masou subsp.	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' Giant 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 auratus 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 reini	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.
'Sujishimadojou' A loach Cobitis sp. 2, subsp. 4	Recently one species has been reclassified into three species and eight subspecies. This is a small subspecies that lives in rivers draining into the lake.
'Sujishimadojou' A loach Cobitis sp. 1	Recently one species has been reclassified into three species and eight subspecies. This is a large species that lives in Lake Biwa and river mouths.
'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' 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' 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. Of the two species of this group that live in Japan, this one is the largest, reaching 255mm across. Used to be important 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' Water plant Vallisneria asiatica var. biwaensis	The leaves have a characteristic twist along their length.
'Sennenmo' Water plant. Potamogeton biwaensis	The leaves don't have a stalk, and are linear with a pointed tip.

Plankton
'Biwakunshoumo' Algae Pediastrum biwae	In Japanese this species is called 'the decoration' due to its shape.
'Biwashibokamuri' Amoebozoa Difflugia biwae	By swallowing sand grains this amoeba produces a hard shell.

Environmental problems:

• Alien species, especially black bass (Micropterus salmoides) and blue gill (Lepomis macrochiru) (right). These fish were introduced into the lake for sport fishing. Both species have dramatically increased their numbers in the lake at the expense of the native fish.
• Poor water quality due to increased nutrient loading leading to eutrophication, algal blooms, red tides and depleted oxygen levels. Housing and farmland that now surround the lake are the major sources.
• Habitat loss, including:
• Loss of 85 % (of area) of attached lakes to construct ricefields since 1940. Attached lakes are crucial for the spawning of some of the endemic and commercially important fish.

• Loss of over 50 % of reed beds in the past 50 years. Reed beds are very important habitat for birds, fish and invertebrates, and also help to remove excess nutrients from the lake.
• Extensive channelization of inflowing streams of rivers. Many streams and rivers are now concrete irrigation ditches with an impoverished fauna and flora. Natural streams and rivers are important for filtering out sediment, excess nutrients and pollution from water before it reaches the lake.
• Land reclamation and development along the shoreline. Approximately one-third of the lake's shore is artificial and major roads run along the edge of the lake.

Have a question about Lake Biwa or the Museum? Visit Question Corner in the Museum or email us: query@lbm.go.jp

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