funded partly by LIFE environment

LIFE environment

Karjaanjoki River Basin

The Karjaanjoki River Basin is the largest river basin in the Uusimaa region, having area over 2000 km². It consists of numerous lakes, rivers and brooks of various types and sizes, which cover 12% of the river basin area in total. Eight municipalities of Uusimaa share this biologically rich area. On its eastern side the esker Lohjanharju, rising over 120 m above the sea level, acts as a watershed. Lakes at the headwater region are located in forested hills up to 130 m above the sea level. The largest lakes in the area freeze around Christmas time and the lakes are free from ice on April.

 Southern part of the river basin is characterised by hemiboreal bioclimatic vegetation zone and the northern part by southern boreal bioclimatic vegetation zone. Forests cover approximately 68 %, cultivated and build-up areas 29 % and peatlands 3 % of the land surface. Pine trees dominate over half of the forested area. The river basin is one of the rainiest regions in Finland and growth season is long. The bedrock in the northern part of the area consists mainly of quartz and feldspar. Granite dominates the southern parts. Lohja area is known for its limestone ground. The soils of the area consist mainly of clay, silt and glacial till.

 The river basin is characterised by the large Lakes Lohjanjärvi (92 km²) and Hiidenvesi (29 km²). In addition, the numerous small lakes and clear- watered rivers form a beautiful mosaic in the headwater region. River Mustionjoki transports water from the river basin to the Pohjanpitäjä Bay area of Gulf of Finland through an old cultivated landscape. The upper reaches of Karjaanjoki River basin consist of three main branches: River Vanjoki and River Vihtijoki which run from the north to Lake Hiidenvesi, and River Nummenjoki which runs to Lake Lohjanjärvi.

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