Lake Abashiri is situated in the northeast part of coastal area of Hokkaido along the Sea of Okhotsk, with 32.5 km² of surface area, 42 km of shoreline, 16.1 m of maximum depth, 7.2 m of mean depth and 0.4 m of altitude. The lake is covered completely with approximately 1 m thick of ice from the midst of December to the midst of April of the next year.

Abashiri River which flow down from the most southern part of catchment area flows into the lake and flows out again from the northeast end of the lake. The river flows into finally the Sea of Okhotsk with 7 km long of flowing down course from the lake. During winter dry season, very high salinity concentration of saline flows backward from the sea very often to Abashiri River and a part of it flows into the lake. Owing to this phenomenon, a very stable hypolimnion is formed in deeper than 10 m layer with approximately 10,000 ppm chlorine concentration of saline.

Judging from the bottom core samples obtained by boring work at the deepest point of the lake, it is considered that a prototype of lake basin was formed at the last Glacial epoch, approximately 20,000 years ago and then present feature of lake was appeared by long corrosion force of Abashiri River at the Holocene epoch, approximately 6,000 years ago. Many remains of Jomon period (an archaeological term designating the Japanese neolithic cultural period extending from about 8,000 B.C. or earlier to about 200 B.C.) are found in the shallow region of estuary of Memanbetsu River.

Recently, replanning of agricultural land has been practiced in the upstream region of Abashiri River and most of rivers and streams were straighten consequently in the catchment area for the development of paddy fields and the repair work of rivers. Since then, however, siltation becomes serious in the estuary. Lowland crop fields along lakeshore were suffered heavy damage from flood in May, 1975. Hereafter, such damage to the wetland of Abashiri Quasi- national Park and camping site of lakeshore is anxious seriously.

Smelt and trout are most important fish in the lake for sport-fishing throughout the season. Eutrophication, however, has progressed recently by the nutrient loading from mainly agricultural land and forest (1, 3, 8).

ILBM (Integrated Lake Basin Management)

Ecosystem Service Features

The lake serves for extensive pond smelt (Hypomesus transpacificus nipponensis) and corbicula (Corbicula japonica) fishing.

The lake also provides for a 1,000 m boat racing course approved by the Japan Boat Association.

Management Challenges

Eutrophication control, cyanobacteria bloom control, blue tides (the decomposed plankton at the sea bottom generates hydrogen sulfide that rises to the sea surface at times of strong winds such as typhoons causing the sea to turn blue).

Management Interventions

A range of technological and managerial interventions have been introduced, financed in large part by the Ministry of Land, Infrastructure, Transport and Tourism, in the name of Clear Stream Renaissance II Project, to reduce nutrient inputs from the lake and inflowing river basins including provision of sewerage service to the four municipalities within the basin.

ILBM Features

The Project was implemented over the period of 2004 and 2014, and the improvement status has been monitored during and after the project, with the involvement of the project implementing agencies and the community stakeholder groups.