Water / Soil / Ground Environment

State of Japan's Environment at a Glance: Japanese Lake Environment - The Central Issue-Eutrophication

The Central Issue - Eutrophication

The following major environmental problems exist in the world's lakes: 1) Eutrophication, 2) Sedimentation, 3) Water Level Reduction, 4) Toxic Waste Pollution, 5) Acidification, and 6) Disturbance of Ecosystem. As seen in the following chart, eutrophication (overabundance of nutrients in lakes, which promotes excessive plant and algae growth) occurs in a large number of Japanese lakes and reservoirs, and the resulting water bloom causes such problems as foul smelling drinking water, fisheries damage, and loss of landscape beauty. Sedimentation has become a problem in some dam reservoirs but is hardly noticeable in natural lakes. Aoki Lake is a good example for the problem of water level reduction because of water being taken for power generation (in this case a 21 meter reduction). Toxic waste pollution levels in lakes are negligible. Tazawa Lake is an example of lake acidification that is caused by acidic water conveyance and linked to the extinction of endemic lake trout. Furthermore, the ecosystems of some lakes have been disturbed by the introduction of exotic fish species for sport fishing.

Utilization Status and Important Environmental Problems of Individual Lakes

Lake NameArea (km2)Water UtilizationConservation Problems
Abashiri L. 32.9 D.A.I.F.T.G.B.N Inland sea-lake with a broad basin. Outbreak of water bloom. Bottom water is becoming anoxic due to back flow of sea water.
Towada L. 59.8 F.T.G.B.P.N. No particular problems. Belongs to the Towada National Park and has 3 million tourists a year.
Yuda R. 6.3 A.T.P. No particular problems. Multi-purposes dam for flood control, power generation and irrigation.
Kamafusa R. 3.9 D.A.I.F.T.G.P.N. An important dam for stable water resource. The environmental project around the dam is being promoted.
Hachiro R. 27.7 D.A.F.T.G. Tendency toward eutrophication shown by water bloom after the construction of a salinity barrier.
Misakubo R. 1.7 D.A.I.G. Since 1988, the water has a moldy odor during spring. An important water source for the domestic and industrial water supply.
Inawashiro L. 103.9 D.A.F.T.S.G.B.P.N. Naturally acidic lake (pH 5) with inflowing rivers. Center of Bandai-Asahi National Park.
Okutadami R. 11.5 F.T.G.B.P.N. No particular problems. The largest artificial lake in Japan. Located in Echigo-Miyama-Tadami Quasi-National Park.
Kasumigaura L. 220.0 D.A.I.F.T.G.B.N. Eutrophic lake with water bloom, moldy water odor, clogging in water purification system, and damage to fisheries. Integrated Measures for Water Quality Conservation being promoted.
Chuzanji L. 11.5 D.F.T.G.B.P.N. The water has an undesirable odor every year since 1981 because of proliferation of the phytoplankton Uroglena.
Oze-numa L. 1.8 F.T.P.N Installation of an integrated septic tank being promoted to reduce the loading from mountain hut.
Inba-numa L. 11.6 .A.I.F.T.G.B.N. Eutrophic lake caused by urbanization in surrounding area. Water bloom and filter clogging in water purification system.
Okutama R. 4.3 D.T.P.N. Eutrophic reservoir with water bloom. Surrounded by resort with valleys.
Sagami R. 3.3 D.A.I.F.T.G.B.P Eutrophic reservoir with moldy water odor, filter clogging in water purification system, water bloom, etc.
Kurobe R. 3.5 A.F.T.P.N. Tourism asset of the Prefecture. Potential problem of environmental degradation caused by tourists.
Kahoku-gata L. 6.1 A.F.T.G.B.N. No particular problems. The use of small-scale integrated septic tanks is being recommended.
Mikata-goko L. 10.1 F.T.G.B.N. Five partially brackish lakes. Scenic damage caused by water bloom.
Yamanaka L. 6.9 A.F.T.G.B.P.N. No particular problems. Domestic effluent is regulated as it penetrates underground after treatment.
Suwa L. 13.3 F.T.G.B. Eutrophic lake caused by industrialization and population growth in the catchment area. Suffers from water bloom in summer.
Agigawa T. 1.6 D.I.F.T.G.B.P. Outbreak of algal bloom in '92 and '93. Multi-purpose dam for flood control, river maintenance, and water supply.
Sanaru L. 1.2 F.T.G.B. Progress of pollution caused by development in surrounding areas up until 1973. Stable water quality in recent years.
Aburaga-fuchi L. 0.6 F.T. Progress of eutrophication caused by urbanization in catchment area. Used for fishing and leisure.
Miyagawa R. 2.0 A.P. No particular problems. Used for irrigation after power generation.
Biwa L. 670.5 D.A.I.F.T.S.G.B.P.N Progress of eutrophication since the 1960s. To achieve certain water quality restoration, a Comprehensive Development Plan with environment construction is being completed.
Hanare L. 0.3 D.F.T.G.B. Saline problem. Popular spot for fishing and leisure.
Yamada-ike R. 0.1 A.T.G. Recreational damage. Water bloom and offensive water odor in summer.
Sengari R. 1.1 D.A.F. Water use damage (offensive water odor, filter clogging in water purification system, and water bloom) has occurred in past.
Kazaya R. 4.5 T.G.P. Temporal outbreak of algal bloom. Artificial lake for power generation only.
Togo-ike L. 4.1 F.T.G.B.N. Pollution caused by visitors to hot spring. Temporal outbreak of water bloom.
Shinji L. 80.3 A.F.T.G.B.N. Deterioration of water quality by socio-economic activities in catchment area. Eutrophication with water bloom in summer.
Kojima R. 10.9 A.F.G.N. Damage to fisheries and agriculture by eutrophication. Decrease of harvests and lower production of rice and lotus roots.
Shinryu R. 0.7 F.T.G.B.P.N. Temporal algal bloom observed. Tourism spot with numerous historic ruins around the lake.
Abu R. 4.2 T.P.N. Air borne dust caused by flood damage lowers tourism value. Temporal algal bloom observed.
Nagayasuguchi R. 2.2 D.A.I.F.T.G.B.P.N. Outbreak of algal bloom in summer. Surrounded by the natural beauty of the Prefectural Natural Park.
Manno-ike R. 1.4 A.F.T.N. No particular problems. Surrounded by areas of historic and traditional value, and the natural beauty changing with the seasons.
Yanase R. 1.6 D.A.I.T.G.P.N. Most of the nutrient loadings are from natural source. Located in a Prefectural Natural Park and visited by many tourists in spring and summer.
Nagase R. 2.1 A.F.G.P. Temporal outbreak of algal bloom from 1976. Natural sources such as mountain forests account for 90% of COD loading.
Hyugakami R. 1.3 A.F.T.G.P.N. Stable water quality. Multi-purpose reservoir for flood control, irrigation, and power generation.
Kitayama R. 2.0 A.T.G.B.P.N. No particular problems. Multi-purpose reservoir for irrigation, power generation, and recreation.
Bessho R. 0.3 D.A.N. No particular problems. Acidity (low pH) caused by two inflowing rivers.
Ichifusa R. 1.7 A.P.N. No particular problems. Flood-control dam for power generation and irrigation.
Serikawa R. 1.4 A.G.B.P. Outbreak of water bloom every year in spring. Multi-purpose dam for power generation, irrigation, and flood control.
Mi-ike L. 0.7 A.F.T.G.B.N. Algal bloom observed from 1988 to 1990. Attracting visitors from inside and outside of the Prefecture.
Ikeda L. 11.0 A.F.T.G.B.N. Deterioration of water quality caused by industrialization in the basin and fishculture in the lake.


L. : Natural Lake R. : Artificial Reservoir
D. : Drinking Water Supply A. : Irrigation
I. : Industrial Water Supply F. : Fisheries
T. : Tourism S. : Swimming
G. : Game Fishing B. : Boating and Yachting
P. : Hydro-power Generation N. : Conservation of Natural Environment