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Lake Annecy EUR-45

Riparian Nation(s) France
Lat. 45°51' N Lng. 6°10' E Alt. 446.5 m
Surface Area 27 km2 Mean Depth 41.5 m Volume 1.12 km3
Shoreline 35 km Catchment Area 278 km2 Residence Time 4 yr
Frozen Period   Mixing Type Monomictic   Morphogenesis/Dam  
Related Info/Site  

Description

Lake Annecy is situated about 30 km south of Geneva in the French Prealps at an altitude of 446.5 m. It has a surface area of 27 km2, a shoreline length of 35 km, and a maximum depth of 64.7 m. Thiou River flows out from the northernmost end of the lake through the town of Annecy, soon joins the Fier River, and finally enters the Rhone River.

The lake measures 14.6 km from north to south, and consists of two basins. The northern main basin, approximately 9.8 km x 3.1 km in size, accounts for about 78% of the whole lake area and volume, while the southern subbasin (4.8 km x 1.5 km) for only 22%. The east and west sides of the lake are guarded by steep mountain slopes which channel prevailing northerly and northwesterly winds over the lake surface.

T>hree main tributary rivers, Eau Morte, Ire and Borette, contribute, respectively, about 42%, 15% and 7% of inflowing water to the lake. Owing to the high carbonate concentration and conductivity of these river water, the lake water maintains relatively high pH values.

Although L. Annecy remained in an oligotrophic condition until the 1940's, the water quality degradation proceeded from the mid 1940's to the 1960's with the increase of human activity around the lake in spite of the relatively small population in the catchment area. In 1967, this process was stopped by the installation of the network of sewage collecting pipes surrounding the lake. Domestic and industrial wastewater were progressively channeled through the pipes to a sewage treatment plant in Annecy outside the lake's catchment. Since then, oligotrophication has been taking place, sustaining the requirement for water quality improvement. In recent years, transparency of the lake water varies from 3 m in summer to 12 m in winter with an annual average of 7.1 m. Summer thermocline occurs between 6 m and 10 m beneath the lake surface.

Extensive limnological studies were made in the lake by many researchers of responsible authorities during the 1960's and 1970's. However, recent researches, especially those from socio-economic approaches, are few (1, 2, 3, 4).

Photo of Lake Annecy
Photo: A. Kurata