Mogami River

It originates from Azuma Volcano on the border between Yamagata and Fukushima prefectures, runs through Yamagata prefecture, and empties into the Sea of ​​Japan at the Shonai Plain. It is one of Japan's largest rivers. Its main river length is 229 km. Its source is the Matsukawa River. It flows down Azuma Volcano and flows almost north, passing through the Yonezawa, Yamagata, and Shinjo basins, then turns west at the Shinjo basin, forming the Mogami Gorge, crossing the Dewa mountain range, emerging from the Shonai Plain, and flowing into the Sea of ​​Japan at the southern part of Sakata City. Its drainage area of ​​7,040 square kilometers accounts for about 75% of the prefecture's total area, and it is the "one river in one prefecture" that flows only through Yamagata prefecture, with most of the prefecture's major cities located on its coast. From the north, the river consists of tributaries such as the Shirakawa River (Okitama Shirakawa River), Sagae River, Su River, Nyu River, Oguni River, Sake River, and Tachiya River, and is characterized by repeated river erosion, transport, and deposition in each basin. The upper reaches of the river are a snowy region that brings abundant water, and the average annual flow rate at Takaya (Tozawa Village) reaches 356 tons per second. On the other hand, from the upper reaches, there are the Imokawa Gorge, the Goten Gorge consisting of three difficult points, Goten, Mikase, and Hayabusa, and the Mogami Gorge. The reason why the Mogami River is said to be one of the three fastest rivers in Japan, along with the Fuji River and the Kuma River, is because these gorges are rapids and there were many difficult points on this large river with thriving shipping.

It is said that shipping on the Mogami River began during the Sengoku period when the Sakata-Shimizu (Okura village) section was developed and Shimizu Riverside was established. After the Battle of Sekigahara (1600), shipping progressed rapidly when Mogami Yoshiaki, who ruled the Shonai region, excavated the Three Difficulties. In particular, Oishida Riverside (Oishida Town), which gained the right to relay river boats from the Kan'ei to Keian eras (1624-1652), developed, and the practice of one-way transportation, with Sakata boats going up and Oishida boats going down, was established. The Oishida Ship Arrangement Office was in charge of managing the Mogami boats in the upper reaches, including Funamachi Riverside (Yamagata City). From the Genroku period (1688-1704), the three river banks of Teratsu (Tendo City), Motodate (Sagae City), and Yokoyama (Oishida Town) were officially recognized due to the prosperity of industry in the upstream area and the excavation of Kurotaki Falls in the upper reaches of the Gohyakugawa Gorge by the Uesugi clan. When the river boat distribution system reached a deadlock, a river boat office was established in Oishida, directly controlled by the shogunate. The main goods transported downstream were rice stored in the river basin domains, merchant rice, safflower, and blue indigo, and upstream were salt, salted fish, used clothing, tea, and small items, mainly transported by hirata boats, and in the later period, small private cormorant fishing boats were also active. However, in the 1890s, with the opening of the Ou Line, the industry rapidly declined. Since then, the Mogami River has played an important role as an agricultural water source irrigating 100,000 hectares of rice paddies, as well as a water supply and industrial water supply. Many dams and power plants have been built, mainly on its tributaries and in the upper reaches. There are also pleasure boats that go down the Mogami Gorge, and efforts are being made to develop green spaces and parks along the river.

The Mogami River is often used as a utamakura (poem of poetry), and the particularly famous verse is "When the Mogami River rises, the rice boats that descend are not in this month" (Kokinshu, Toka). In addition, the river has been closely associated with writers and poets such as Basho and Saito Mokichi.

[Shige Nakagawa]

"The Mogami River, The Flow of the Best (1982, Yamagata Prefectural General Academic Research Office)" ▽ "The Mogami River by Inoue Hachizo (1982, Sobunsha)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

山形・福島県境の吾妻火山(あづまかざん)に源を発し、山形県内を貫流し庄内平野(しょうないへいや)で日本海に注ぐわが国有数の大河。一級河川。幹線流路延長229キロメートル。源流は松川という。吾妻火山を流下してほぼ北流、米沢(よねざわ)、山形、新庄(しんじょう)の各盆地を貫流し、新庄盆地で向きを西に変え、最上峡をつくって出羽(でわ)山地を横切り、庄内平野に出て酒田市南部で日本海に流入する。流域面積7040平方キロメートルは県総面積の約75％を占め、しかも山形県内だけを流れる「一県一河川」であり、県内の主要都市のほとんどが沿岸に立地する。北から白川（置賜白(おきたましら)川）、寒河江(さがえ)川、須(す)川、丹生(にう)川、小国(おぐに)川、鮭(さけ)川、立谷(たちや)川などの支流をあわせ、盆地ごとに河川の侵食、流送、堆積(たいせき)の作用を繰り返すという地形的特色を示す。上流域は多雪地で豊かな水量をもたらし、高屋（戸沢村）の年平均流量は毎秒356トンに達する。一方、上流から五百川峡(いもかわきょう)、碁点(ごてん)・三ヶ瀬(みかのせ)・隼(はやぶさ)の三難所からなる碁点峡、最上峡などがあり、最上川が富士川、球磨(くま)川とともに日本三急流の一つといわれるのは、これらの峡谷部が急流で、舟運の盛んな大河としては難所が多かったことによる。

　最上川の舟運は戦国時代に酒田―清水(しみず)（大蔵(おおくら)村）間が開発され清水河岸(かし)が置かれたのが端緒という。関ヶ原の戦い（1600）後、庄内地方を領有した最上義光(よしあき)によって三難所が開削されて急速に進展した。とくに寛永(かんえい)年間～慶安(けいあん)年間（1624～1652）にかけて川船中継権を獲得した大石田河岸（大石田町）が発達し、上り酒田船、下り大石田船という片運送の慣行も成立した。船町(ふなまち)河岸（山形市）など上流地域の最上船も含め大石田船差配役が統轄した。元禄(げんろく)年間（1688～1704）以降は上流地域の産業の隆盛や上杉藩による五百川峡上流部の黒滝の開削などで寺津(てらつ)（天童市）、本楯(もとだて)（寒河江市）、横山（大石田町）の三河岸も公認された。川船差配制が行き詰まると大石田には幕府直轄の川舟役所が設置された。おもな運送物資は、下り荷に流域各藩の蔵米、商人米、紅花、青苧(あおそ)など、上り荷は塩、塩魚、古手(ふるて)、茶、小間物などで、主として艜船(ひらたぶね)で運ばれ、後期には私船の小鵜飼(こうがい)船も活躍した。しかし明治30年代に入ると奥羽線の開通などで急速に衰退した。その後最上川は10万ヘクタールの水田を潤す農業用水源として、また上水道、工業用水として重要な役割を担うことになった。支流や上流部を中心にダム、発電所が多く設置されている。一方、最上峡舟下りの遊覧船などもあり、河川緑地、公園の整備も図られている。

　なお、最上川は歌枕(うたまくら)として多く詠まれており、とくに「最上河のぼればくだる稲舟のいなにはあらずこの月ばかり」（『古今集』東歌）は名高い。このほか、芭蕉(ばしょう)、斎藤茂吉(もきち)など文人、墨客とのかかわりも深い。

［中川　重］

『『最上川』『最上のながれ』（1982・山形県総合学術調査室）』▽『井上八蔵著『最上川』（1982・叢文社）』

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