Lake Nojiri ASI-43

Lat.36.826 Lng.138.222 Alt.654
Riparian Nation(s) Japan
Surface Area 5 km2 Mean Depth 21 m Volume 0.09 km3
Shoreline 13.6 km Catchment Area 8.24 km2 Residence Time 2 yr
Frozen Period Jan-Mar Mixing Type Dimictic Morphogenesis/Dam Volcanic (damming)
Related Info/Site Myoko-Togakushi renzan National Park (2015)

Description

Lake Nojiri is a dammed lake formed by the debris ejected from the volcano Mt. Kurohime located to the west of the lake. The southern part of this picturesque mountain lake, resembling a hibiscus flower in its outline, began to develop into a resort area as early as in the Taisho era (1912-1926). The lakeshore has become further intensively used to accommodate resort facilities and recreational activities, and now accepts 750,000 visitors annually.

The lake water flows out through the R. Ikejiri, which has been a source of irrigation water since 17th century. It was also one of the water sources of Nagano City, supplying 10,000 tons day-1 of water to the city from 1954 to 2005 except for the summer season between June and September. The fishery on the lake provides rich fish harvest including wakasagi (Hypomesus transpacificus) and dace (Leuciscus hakonensis). Aside from water supply, fishery and recreation, power generation is also an important use of the lake water. The fossils of Naumann elephant, known to have lived some 20,000 years ago, are excavated frequently from the lake's shallow bottom.

The lake has no large inflowing stream and is mainly fed by underground water. Therefore, the lake had long remained oligotrophic, but the use of the lake water for hydroelectric power generation led to a wide range of water level fluctuation, and this, together with lakeshore development, is mainly responsible for increasing trend of pollution. (1987, revised in 2018)

Around 1975, when water plant is abundant in the lake, the rise of elodea obstructed navigation and interfered with fishing so that grass carps are released to eliminate elodea. It took about three years to eradicate the plant. Afterwards red tide began to appear due to anthropogenic activities and made it necessary to prepare a measure to improve water quality. For this reason Lake Nojiri was appointed to the tenth designated lake (the second in Nagano Prefecture), in October 1994, based on the Law Concerning Special Measures for Preserving Lake Water Quality. The Phase V Water Quality Conservation Plan covers from FY 2014 to FY 2018.

Although various measures to preserve good water quality were taken according to the plan, COD did not achieve the environmental reference point and is leveling off or slightly increasing, and the T-N and T-P are leveling off in recent years. As Lake Nojiri does not have much water plant due to the grass carp released in the plast, the Lake Nojiri Water Plant Restoration Study Group, public-private collaboration entity, is experimenting with a restoration of Nitellopsis obtuse which previously existed in the lake.

Since 1991 the Lake Nojiri Clean Rally is convened every year as part of environmental education efforts for school children and local residents, observing the lake on a cruising boat, and fostering the deeper understanding of the conservation of water environment by studying these items like water quality, water plant and grass carp. (2018)

Photo of Lake Nojiri
Photo: A. Kurata