Lake Biwa

Japanese: 琵琶湖 - びわこ

A fault-caused lake in the center of Shiga Prefecture, it is the largest lake in Japan. One of the oldest lakes in the world, Ko-Lake Biwa was formed around 5 million years ago near Iga-Ueno in Mie Prefecture, and is said to have moved north due to subsequent crustal movements, reaching its current position around 1.2 million years ago. Generally speaking, lakes become shallower over the years due to the inflow of sediment, eventually turning into marshes and ending their lifespan, but Lake Biwa has maintained its longevity due to the continuous subsidence of its base caused by the basin-forming movement of the earth's crust. It has an area of approximately 674 square kilometers, a shoreline length of approximately 235 kilometers, a lake surface elevation of 85 meters, a maximum depth of 103.8 meters, an average depth of 40 meters, a volume of 27.5 billion cubic meters, a catchment area of 3,848 square kilometers, a long axis of 63.5 kilometers between Shiotsu, Nishiasaicho, Nagahama City and Tamanoura, Otsu City, a maximum width of 22.1 kilometers between Shimosakahamacho, Nagahama City and Shinasahicho, Takashima City, and a minimum width of 1.4 kilometers near the Lake Biwa Bridge. There are ten lakes in Japan with a maximum depth of over 100 meters, but only Lake Biwa is a tectonic lake formed by crustal movement; all the others are caldera lakes formed by the collapse of a crater. Lake Biwa's area accounts for about one-sixth of the prefecture's land area, and its catchment area covers almost the entire prefecture. As a result, all of the prefecture's rivers, namely the Yasu River, Hino River, Aichi River, Inukami River, Ane River, Azumi River, and 125 other first-class rivers (including tributaries, the total number is about 2,000), all flow into Lake Biwa. However, the only outlets from Lake Biwa are the Seta River and the Lake Biwa Canal, and the flow rate can be controlled by installing sluice gates at these two outlets.

Lake Biwa can be roughly divided into two parts: the North Lake (main lake basin, large lake) and the South Lake (secondary lake basin), which are separated by the delta of the Yasu River. The North Lake is an oligotrophic lake with an average depth of about 43 meters and a transparency of 7 to 10 meters, while the South Lake is a eutrophic lake with a maximum depth of 4 meters and a transparency of 2 to 3 meters, showing a stark contrast. There used to be many inner lakes (affiliated lakes) on the lake shore, such as Lake Dainakano and Lake Matsubara-naiko, but most of them have disappeared due to reclamation after World War II.

[Seiichi Takahashi]

history

Lake Biwa was formerly called Oumi, Oumi Lake, and Nihonoumi (Nihon is another name for the grebe). Oumi means a freshwater lake, and is the origin of the name Omi Province, which is closer to the capital than Totomi Province (Shizuoka Prefecture, Lake Hamana). Kakinomoto no Hitomaro's famous poem, "Oumi no Umi Yuu Waves Chidori Na ga Nareba Kokoro wa shinnita wa ... Lake Biwa has been mentioned in many literary works since ancient times, such as the Kojiki, Sarashina Nikki, Tokan Kiko, and Makura no Soshi, and there is also a legend that it was formed overnight along with Mount Fuji. Lake Biwa has been loved since ancient times, and because it is located almost in the center of Japan, it has also played an important role in history. Jomon and Yayoi period ruins have been discovered at the bottom of the lake, and water transportation on Lake Biwa has been a means of transportation connecting Kyoto and Osaka with the northern and eastern provinces since ancient times, and has been extremely important up until modern times.

[Seiichi Takahashi]

Biology

The water temperature of Lake Biwa is about 30°C at the surface in summer and about 6°C at the minimum in winter, so it does not freeze. As a result, the lake is home to many endemic species, including both warm-water and cold-water fish. The fishing industry is therefore active, and unique fishing methods have been developed. In particular, the fishing method seen near the lake shore, in which fish are chased into bamboo fences, is one of the Lake Biwa scenery. The Gengoro-buna (carp), Honmoroko (carp), Isaza (carp), Koayu (fish), Lotus (lotus), and Wataka (sea cucumber) are endemic species, and Koayu caught in Lake Biwa are released into rivers all over the country. There are also many types of shellfish, and in particular the Ikechogai (sea mussel) is actively cultivated as the mother shell of freshwater pearls, and the Seta corbiculatus is also famous. In addition to fish and shellfish, the reeds that grow on the lake shore have also been used as material for making Yoshizu (rice screens). Lake Biwa is indeed a lake of bountiful blessings. However, in recent years, the decline of endemic species due to the release of non-native species such as black bass has become an issue.

[Seiichi Takahashi]

sightseeing

Lake Biwa has been filled with the blessings of nature, but at the same time, it has also produced beautiful landscapes. The changing seasons of the mountains, plains, and lake are depicted in the "Eight Views of Omi" and "Eight Views of Lake Biwa," and have captivated the hearts of many travelers since ancient times. Lake Biwa Quasi-National Park, the first quasi-national park to be designated as such, is home to a wealth of cultural assets, such as Tsukubusuma Shrine on Chikubu Island, which floats in the lake amidst diverse nature, and is one of Japan's leading tourist destinations. Starting with Mt. Hiei Driveway, which opened in 1958, the Lake Biwa Ohashi Bridge, Mt. Ibuki Driveway, Oku-Hiei Driveway, Oku-Biwako Parkway, and Omi Ohashi Bridge have been constructed or opened, and tourism development has been carried out, such as the launch of sightseeing boats on the lake, and the number of tourists visiting Lake Biwa is increasing year by year. Lake Biwa is also used as a place for sports such as swimming and yachting.

[Seiichi Takahashi]

development

Lake Biwa is often called the "water reservoir of the Kinki region." It supplies drinking water to 13 million people downstream, and there is probably no other lake in the world that brings blessings to so many people. It has been used since ancient times not only for drinking water, but also for industrial and agricultural use. On the other hand, the area around the lake has been plagued by floods and droughts caused by fluctuations in the lake water level. Therefore, various construction works and plans have been carried out to control and develop the lake. Representative examples include the irrigation of the Seta River from the early modern period to the Meiji period, the opening of the Lake Biwa Canal in 1890 (Meiji 23), the completion of the Nango Araiseki Weir in 1905, and the completion of the Shin-Araiseki Weir in 1961 (Showa 36). In 1972, the Lake Biwa Comprehensive Development Special Measures Act was enacted, and plans are being made to comprehensively address water utilization, flood control, and conservation. However, the situation surrounding Lake Biwa remains severe. Lake Biwa was once a representative oligotrophic lake, but with the urbanization and industrialization of the coastal areas triggered by the high economic growth period in the 1960s, the southern lake has turned into a eutrophic lake, and the northern lake is also in the process of becoming eutrophic. As symbolized by the occurrence of red tides, the lake water is becoming rapidly polluted. Although measures have been taken to address this, such as the enactment of the Lake Biwa Ordinance (Shiga Prefecture Ordinance on the Prevention of Eutrophication of Lake Biwa) in 1979, the current situation is far from a fundamental solution. In addition, the World Lake Environment Conference was held in Otsu City in 1984, and the Lake Biwa Declaration was adopted, which included the establishment of the World Year of Lakes. In 1993, it was registered as a Ramsar Convention wetland. In the same year, the public interest corporation "Lake Biwa and Yodo River Water Quality Conservation Organization" was established. Furthermore, a long-term conservation and improvement plan for Lake Biwa (Mother Lake 21 Plan) is being promoted from 1999 to 2020. Cultural and research facilities related to Lake Biwa include the Lake Biwa Museum (Kusatsu City), Lake Biwa Environmental Science Center (Otsu City), and Lake Biwa Waterfowl and Wetlands Center (Nagahama City).

[Seiichi Takahashi]

"A Literary Walk around Lake Biwa" by Senga Koichi (1973, Shintankasha)" ▽ "Lake Biwa I & II" edited by Shiga University Lake Research Institute (1974, Sankyo Publishing)" ▽ "Living Fossil Lake" edited by Shiga Geological Research Association (1977, Horitsu Bunkasha)" ▽ "A Tour of Lake Biwa" edited by Fujioka Kenjiro (1980, Nakanishiya Publishing)" ▽ "Lake Biwa" edited by the Lake Biwa Editorial Committee (1983, Sunbright Publishing)" ▽ "Folklore of Lake Biwa" by Hashimoto Tetsuo (1984, Bunka Publishing Bureau)" ▽ "Thinking about the Earth from the Shores of Lake Biwa" by Suzuki Norio (1992, Shinsou Publishing)" ▽ "Lake People - The Story of Lake Biwa and Life" (1996, Shiga Prefectural Lake Biwa Museum Opening Commemorative Magazine Editorial Committee) " Yosuke Imamori, "Fish of Lake Biwa" (2001, Kaiseisha)

Lake Biwa
View from Mt. Hiei. Otsu City is in the foreground, and Kusatsu City is on the opposite bank. Lake Biwa Quasi-National Park. Shiga Prefecture © Lake Biwa Visitors Bureau .

Lake Biwa

Takeo Island
Located in the north of Lake Biwa, south of Katsuragi-ozaki (photo left), this small island (photo right) is about 2km in circumference. Since ancient times, its mysterious appearance has attracted faith as a paradise and a spiritual land. On the island are Tsukubusuma Shrine, Bentendo, which is considered one of the three Benten shrines in Japan, and Hogon-ji Temple, the 30th temple of the 33 Saigoku Pilgrimage Sites. "Fresh greenery and the sunken reflection of Chikubushima Island" is counted as one of the eight scenic spots of Lake Biwa. Nationally designated historic site Nationally designated place of scenic beauty Nagahama City, Shiga Prefecture © Fujino Yuya ">

Takeo Island

Tsukufusuma Shrine
Main hall (national treasure). Nagahama City, Shiga Prefecture © Nagahama Tourism Association ">

Tsukufusuma Shrine

"One of the famous places in the capital: View of the lake from the top of Mt. Hiei"
Painting by Hasegawa Sadanobu (first generation) National Diet Library

"One of the famous places in the capital: View of the lake from the top of Mt. Hiei"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

滋賀県の中央部にある断層陥没湖で、日本最大の湖。世界有数の古い湖で、古琵琶湖は500万年ほど前に三重県伊賀上野付近で誕生し、その後の地殻変動によって北へ移動し、約120万年前にほぼ現在の位置に達したといわれる。一般的にいって、湖は長年の間に土砂の流入によって浅くなり、最後には湿地化してその寿命を終えることが多いが、琵琶湖の場合は、地殻の造盆運動によって基盤が沈降し続けている関係で長寿を保っているわけである。面積約674平方キロメートル、湖岸線延長約235キロメートル、湖面標高85メートル、最大水深103.8メートル、平均水深40メートル、容積275億立方メートル、集水面積3848平方キロメートル、長軸は長浜(ながはま)市西浅井町塩津(にしあざいちょうしおつ)と大津市玉野浦の間で63.5キロメートル、最大幅は長浜市下坂浜(しもさかはま)町と高島市新旭(しんあさひ)町の間で22.1キロメートル、最小幅は琵琶湖大橋付近で1.4キロメートルである。日本には最大水深100メートル以上の湖が10あるが、琵琶湖のみが地殻の変動によって形成された構造湖で、ほかはすべて火口の陥没によるカルデラ湖である。琵琶湖の面積は県の面積の約6分の1を占め、その集水域は県のほぼ全域と一致する。したがって、県内の河川、すなわち野洲(やす)川、日野川、愛知(えち)川、犬上(いぬかみ)川、姉(あね)川、安曇(あど)川などの125にも及ぶ一級河川（支流をも含めると約2000にも達する）は、すべて琵琶湖に注ぎ込んでいることになる。これに対して、琵琶湖からの流出口は瀬田川と琵琶湖疏水(そすい)のみで、この二つの流出口に水門を設けることによって、流量の制御が可能である。

　琵琶湖は大きく二つに分けられる。野洲川の三角州を境とする北湖（主湖盆、太湖）と南湖（副湖盆）がそれである。北湖は平均水深約43メートルで透明度も7～10メートルの貧栄養湖であるのに対し、南湖は最大水深が4メートル、透明度も2～3メートルの富栄養湖という好対照を示す。また、かつては大中(だいなか)之湖や松原内湖などの内湖（付属湖）が湖岸に数多く存在していたが、第二次世界大戦中以後の干拓などによって大部分が消滅した。

［高橋誠一］

歴史

琵琶湖は、古くは、淡海(おうみ)、近江(おうみ)之湖、鳰の海(にほのうみ)（鳰はカイツブリの別名）などとよばれた。淡海は淡水湖を意味し、遠江(とおとうみ)国（静岡県、浜名湖）に対して、都に近い淡水の「近つ淡海の国」すなわち近江国の地名の起源ともなった。柿本人麻呂(かきのもとのひとまろ)の「淡海の海夕浪千鳥汝(な)が鳴けば心もしのにいにしへ思ほゆ」（『万葉集』巻3）は有名。「琵琶湖」の名称がいつごろから一般化したかについては明らかではないが、楽器の琵琶に形が似ていることから名づけられたともいわれる。古来、『古事記』『更級(さらしな)日記』『東関(とうかん)紀行』『枕草子(まくらのそうし)』など多くの文学作品に記載され、また富士山とともに一夜にしてできたとの伝説もある。このように古くから親しまれてきた琵琶湖は、日本のほぼ中央部に位置していることもあって、歴史上も重要な役割を果たしてきた。湖底には縄文・弥生(やよい)時代の遺跡も発見されているし、また琵琶湖の水上交通は、古くから京、大坂と北国、東国を結ぶ交通手段で、近代に至るまできわめて重要であった。

［高橋誠一］

生物

琵琶湖の水温は、夏季の最高が表面で約30℃、冬季の最低が約6℃であるため結氷しない。そのために、この湖の生物には固有種が多く、暖水・冷水両魚類が生息している。したがって、漁業は活発で、独特の漁法を生み出してきた。とりわけ、湖岸近くにみられる竹の簀(す)を張り巡らして魚類を追い込む魞(えり)漁は、琵琶湖の風物詩の一つともなっている。ゲンゴロウブナ、ホンモロコ、イサザ、コアユ、ハス、ワタカなどは特産種であり、琵琶湖でとれたコアユは全国各地の河川に放流される。また貝類の種類も多く、とくにイケチョウガイは淡水真珠の母貝として盛んに養殖されており、セタシジミも有名である。魚貝類だけでなく、湖岸に生育するアシ（ヨシ）もよしずなどの材料として利用されてきた。まさに琵琶湖は豊かな恵みの湖である。しかし、近年ではブラックバスなどの外来種の放流による固有種の減少が問題とされている。

［高橋誠一］

観光

琵琶湖は自然の恵みに満ちあふれてきたが、同時に、それは美しい景観をも生み出してきた。山と平野と湖が季節のなかで示す移ろいは、「近江八景」や「琵琶湖八景」にも表現され、古来多くの旅人の心をとらえてきた。国定公園としては最初に指定された琵琶湖国定公園は、多様な自然のなかに湖中に浮かぶ竹生(ちくぶ)島の都久夫須麻(つくぶすま)神社など豊富な文化財をも有しており、わが国でも有数の観光地となっている。1958年（昭和33）開通した比叡山(ひえいざん)ドライブウェイをはじめとして、琵琶湖大橋、伊吹山(いぶきやま)ドライブウェイ、奥比叡ドライブウェイ、奥琵琶湖パークウェイや、近江大橋などが築造または開通し、湖上の観光船の就航などの観光開発も行われて、琵琶湖を訪れる観光客は年々増加している。また、水泳やヨットなどのスポーツの場としても利用されている。

［高橋誠一］

開発

琵琶湖はよく「近畿の水がめ」といわれる。下流域の1300万人もの人たちの飲料水を供給しているわけで、これほど多くの人に恵みをもたらしている湖は、おそらく世界に例をみないであろう。飲料水だけではなく、工業・農業用水としても古くから利用されてきた。その反面、湖周辺は湖水の変動による洪水や渇水に悩まされてきた。したがって、琵琶湖の治水と開発をめぐって、さまざまな工事と計画が実施されてきたのである。近世から明治にかけての瀬田川の川ざらえ、1890年（明治23）琵琶湖疏水(そすい)の開通、1905年南郷洗堰(なんごうあらいぜき)の完成、1961年（昭和36）の新洗堰の完成などが、その代表的なものである。また、1972年には琵琶湖総合開発特別措置法が立法化され、利水、治水、保全を総合的に解決しようとする計画も進められている。しかし、琵琶湖を取り巻く情勢はなお厳しい。すなわち、かつては代表的な貧栄養湖であった琵琶湖が、1960年代の高度経済成長期を契機とする沿岸の都市化、工業化の進展によって、南湖は富栄養湖に転じ、北湖も富栄養湖へ移行しつつある。赤潮の発生などに象徴されるように、湖水の汚濁が急激に進みつつあるわけで、これに対して1979年には「琵琶湖条例」（滋賀県琵琶湖の富栄養化の防止に関する条例）が制定されるなどの対策が講じられてはいるものの、抜本的な解決にはほど遠い現状である。なお、1984年大津市で世界湖沼環境会議が開かれ、世界湖沼年の設定などを内容とする「琵琶湖宣言」が採択された。1993年（平成5）には、ラムサール条約登録湿地となった。同年には公益法人「琵琶湖・淀川水質保全機構」が設立されている。さらに1999年から2020年までの長期にわたり、琵琶湖の保全整備計画（マザーレイク21計画）が推進されている。なお、琵琶湖に関する文化・研究施設には、琵琶湖博物館（草津市）、琵琶湖環境科学センター（大津市）、琵琶湖水鳥・湿地センター（長浜市）などがある。

［高橋誠一］

『千賀浩一著『琵琶湖文学散歩』（1973・新短歌社）』▽『滋賀大学湖沼研究所編『びわ湖Ⅰ・Ⅱ』（1974・三共出版社）』▽『滋賀地学研究会編『生きている化石湖』（1977・法律文化社）』▽『藤岡謙二郎編『びわ湖周遊』（1980・ナカニシヤ出版）』▽『琵琶湖編集委員会編『琵琶湖』（1983・サンブライト出版）』▽『橋本鉄男著『琵琶湖の民俗誌』（1984・文化出版局）』▽『鈴木紀雄著『琵琶湖のほとりから地球を考える』（1992・新草出版）』▽『『湖人――琵琶湖とくらしの物語』（1996・滋賀県立琵琶湖博物館開館記念誌編集委員会）』▽『今森洋輔著『琵琶湖の魚』（2001・偕成社）』

[参照項目] | 姉川 | 愛知川 | 近江八景 | 構造湖 | 滋賀（県） | 瀬田川 | 竹生島 | 琵琶湖国定公園 | 琵琶湖湖底遺跡 | 琵琶湖疏水 | 野洲川

琵琶湖

竹生島
琵琶湖北部、葛籠尾崎（写真左）の南に位置する周囲約2kmの小島（同右）。古来、神秘的なその姿から仙境、霊境として信仰を集めた。島内には、都久夫須麻神社、日本三弁天の一つとされる弁天堂、西国三十三所第30番札所の宝厳寺がある。「新緑・竹生島の沈影」は琵琶湖八景の一つに数えられる。国指定史跡　国指定名勝　滋賀県長浜市©藤野優哉">

竹生島

都久夫須麻神社

『都名所之内　比叡山山上より湖水を望』
長谷川貞信（初世）画国立国会図書館所蔵">

『都名所之内　比叡山山上より湖水を望』

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