Lake Kasumigaura

Lake Kasumigaura. It is the second-largest lake in Japan by surface area, located entirely within Ibaraki Prefecture east of Tokyo. Originally a brackish lagoon connected to the Pacific Ocean, it was converted into a freshwater lake in the 20th century. The lake is a vital resource for the Kantō region, supporting agriculture, industry, and local communities while facing significant environmental challenges.

Geography and Hydrology

The lake system comprises three main water bodies: the large Kita-ura, the smaller Naka-ura, and the western Sō-ura. It is a shallow basin with an average depth of only four meters, fed primarily by the Sakura River and the Koise River. The sole natural outlet is the Hitachitone River, which flows into the Pacific Ocean near Kamisu. The surrounding topography is part of the Jōsō Plateau, and the lake's watershed extends across southern Ibaraki Prefecture. Key settlements on its shores include the cities of Tsuchiura and Kasumigaura, and the towns of Ami and Inashiki.

History and Formation

The lake basin was formed by crustal movement and was originally an inner bay of the Pacific Ocean, as evidenced by shell mound discoveries from the Jōmon period. During the Edo period, it was a significant transport route for goods to Edo via the Tone River water system. A major transformation began in 1963 with the construction of the Hitachitone Floodgate, completed in 1971, which cut off seawater inflow. This project, driven by land reclamation and freshwater demand for the Kashima Industrial Zone, officially converted it into a freshwater lake. Further engineering included the Kasumigaura River Work to manage water levels.

Ecology and Environmental Issues

The shift to freshwater created a eutrophication crisis, with severe blue-green algae blooms occurring annually since the 1970s due to nutrient runoff from intensive agriculture in the watershed. This has degraded water quality and impacted native species. The lake is a critical habitat for migratory birds, including the endangered white-naped crane, and is designated a Ramsar site under the Ramsar Convention. Invasive species like the largemouth bass and bluegill have disrupted the indigenous ecosystem, outcompeting native fish such as the icefish and crucian carp.

Economic and Recreational Use

The lake is a cornerstone of regional agriculture, supplying irrigation water for the extensive paddy fields that produce Koshihikari rice. It supports commercial fishery for species like corbicula clam and smelt, though catches have declined. The Kashima Industrial Zone and local municipalities rely on it for industrial and domestic water. Recreational activities include sailing, with the lake hosting events for the 1964 Summer Olympics and being a training site for the Japan Sailing Federation. The scenic Kasumigaura Cycling Road and annual Tsuchiura Fireworks Festival are major tourist attractions.

Management and Conservation

Management is guided by the national Law Concerning Special Measures for Conservation of Lake Water Quality and the prefectural Ordinance for the Conservation of the Water Quality of Lake Kasumigaura. The Ministry of Land, Infrastructure, Transport and Tourism and the Ibaraki Prefectural Government lead efforts, including the construction of the Kasumigaura Water Conveyance Channel to introduce cleaner water from the Tone River. Conservation projects focus on reducing nutrient loads through improved agricultural practices and riparian buffer zones. Research is conducted by the National Institute for Environmental Studies and the Fisheries Research Agency to monitor ecosystem health and restore native fisheries.

Category:Lakes of Japan Category:Ibaraki Prefecture Category:Ramsar sites in Japan