+Lake Batur is the largest and deepest confined lake in Bali, and its basin is a caldera. It is situated next to the volcano Gunung Batur. The most recent eruption happened in 1963. There is some small scale agriculture around the lake, and an increasing number of guest houses are being built. The lake is also used for fisheries. The volcano is a favored hiking area, and on the western shore there is the oldest village in Bali, Trunyan. By now, there are no major man-caused threats to the lake. A survey has been made on the flood control regulation (DPU and Exsa International 1981). The lake was variously stratified during the visits (RTR 8.9, 48.0 and 126.9), and there were indications that it may have had a full circulation in July 1993 (see also Ruttner 1931, Green et al. 1994). However, Schmitz (1994) is claiming that Batur lake is both thermo- and chemostratified, although his studies were only to the depth of 50 meters. It is the most saline of the studied lakes, having a conductivity of 1,750-1,800 µS/cm, and a dissolved solids concentration of 1,340-1,520 mg/l. It has also the highest alkalinity (3.60-3.70 meq/l) and high pH (8.8), especially in the epilimnion. There was no carbon dioxide in the lake, and iron and manganese concentrations were not elevated near the bottom. The concentrations of calcium, chloride, potassium, sodium, magnesium and sulfate were high. Nutrient concentrations of the lake were rather low, total nitrogen from 0.256 to 0.970 mg/l N and total phosphorus from undetectable to 0.028 mg/l P. Chlorophyll a concentrations were from 0.57 to 3.83 mg/m³. The phytoplankton composition was rather diverse, but the diatom Synedra acus v. angustissima was dominant in September 1992. The total biomass was 2.4 mg/l, and transparency from 3.0 to 3.2 meters. The lake is considered to be oligotrophic, with signs of eutrophication. According to the Indonesian national standards water is not suitable for drinking and other purposes.

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