Lake Brienz, Switzerland

Ultra-oligotrophic Lake Brienz, situated in the front ranges of the Swiss Alps at 564 m asl (maximum depth 260 m, area 30 km2), is dominated by two major inflows, the rivers Aare and Lütschine. These rivers transport annually over 300’000 tons of suspended material into the lake. Only 3% of this suspended material is transported through the outflow, while the rest sediments into the lake. The Lütschine catchment is mostly composed of limestone, whereas the Aare has primarily a crystalline geology. Investigations show a maximum concentration of suspended particles of 18-26 mg/l (dry weight) in the upper layer of the lake in late August and early September, whereas normal concentrations were only 4-8 mg l/l in summer and 1-3 mg l/l in winter. Epilimnetic temperatures in the lake reach 17-20°C in summer.