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Limnological features of Lake Puma Yum Co, a typical alpine lake located at the altitude of 5030 m in the Tibetan Plateau, China, are described based on the fi ndings of the second expedition in September 2004. The lake surface is about 280 km 2 and maximal depth is 65 m. Total infl ow just after the rainy season was estimated to be about 860 000 m 3 day, and the lake water was drained from a newly excavated channel at a rate of 960 000 m 3 day −1. We may have to expect undesirable lowering of the water level by this new drainage, especially in the dry season. Thermocline developed from 20 to 30 m depth, and the euphotic zone reached the 50 m depth. Dissolved oxygen in surface water was supersaturated as in productive lakes, although there were no large point and nonpoint sources of nutrient in the catchment. Vertical distribution of phytoplankton biomass and primary production suggested the presence of photoinhibition. What should be noted about the fl ora and fauna is that a Chara zone and a shell zone were distributed at about 30 or 40 m of depth.

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