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Lake Inba

Lake in Chiba Prefecture, Japan

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It is a popular location for outdoor activities, including fishing, bicycling, and birding, and is home to numerous species of plants, birds, and other wildlife. The National Museum of Japanese History is located on the grounds of the ruins of Sakura Castle, southwest of the lake. It is easily accessible through a number of train and bus services.

The lake is also variously known as Lake Imba, Lake Imbanuma, Inbanuma, and Imbanuma.

Geography and history

Lake Inba is located in Inba Tega Prefectural Natural Park, and is the largest lake in Chiba Prefecture, with an original surface area of 25.8 square kilometres (10.0 mi2). It is a man-made lake created by the natural damming of a small valley, and it is the largest lake in Chiba Prefecture. The lake is within the Shimōsa Plateau, which covers most of northern part of the prefecture. After multiple land reclamation projects, similar to those carried out on Lake Teganuma, its surface area was significantly reduced to about 13.1 square kilometres (5.1 mi2), before being further reduced to 9.43 square kilometres (3.64 mi2).

About 1000 years ago, the Tone River flowed into what is now Tokyo Bay, and the area where Lake Inba is now located was part of the inland Katori Sea and was called Inbaura (印旛浦). As part of a large project to control flooding in the Tokyo area during the Edo Period, the river's course was diverted to flow into the Pacific Ocean, with its mouth now at Chōshi. The Katori Sea was slowly filled in and the remaining water and land desalinated, and a large swampy area that eventually drained into Tokyo Bay was created.

Lake Inba was a large, swampy area containing a W-shaped lake of about 25.8 square kilometres (10.0 mi2) until the 1930s. A project completed in 1949 reduced the surface area of the lake almost in half, and split the lake into northern and western sections connected by the Inba Cutoff Canal (印旛捷水路, Inba Shōsuiro). The Inba Cutoff Canal is listed as one of the top 100 canals in Japan. The northern section reaches depths of 4.8 metres (16 ft), while the western section is shallower at about 2.9 metres (9 ft 6 in) maximum depth. A reclamation project completed from 1963 to 1969 developed additional water resources, improved area rice fields, and better managed flooding. The lake contains no islands.

Due to population increases in the area during the 1970s, nutrient runoff into the lake began causing blue-green algae blooms, an increase in water chestnut growth, and municipal water odors. Various education programs and better handling of wastewater have reduced these issues.

The lake spans multiple municipalities, including the cities of Inzai, Narita, Sakura, and Yachiyo, and the town of Sakae. The drainage basin, which spans 494 square kilometres (191 sq mi), includes these municipalities as well as the cities of Chiba, Funabashi, Kamagaya, Yotsukaidō, Yachimata, Shiroi, and Tomisato, and the town of Shisui. The population found within the lake's basin is about 794,000 as of 2020.

There are numerous rivers that empty into Lake Inba. These include the Nagato River, Kashima River, Moroto River, Takasaki River, Teguri River, Kanzaki River, Kannō River, and Shin River. The lake holds a water volume of about 19,700,000 cubic metres (700,000,000 cu ft), and each year supplies about 34,831,000 cubic metres (45,557,000 cu yd) of potable water, 47,368,000 cubic metres (61,955,000 cu yd) of water for industrial uses, and 76,876,000 cubic metres (100,550,000 cu yd) for agricultural uses.

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