Two surveys were conducted during November to December in 2007 and June to August in 2008. Five lakes (Lake Dianchi, Lake Fuxian, Lake Yangzonghai, Lake Xingyun and Lake Qilu) were sampled in the first survey, while all thirteen lakes were included in the second survey (Fig. 1).
The studied lakes are small to medium-sized tectonic lakes with a maximum depth from 5 m to 150 m (Table 1). The substratum of those lakes is mainly silt, clay or sandy clay.
Sampling sites were distributed uniformly in study lakes and covered all kinds of habitats. Molluscs were collected using a triangular dredge and a weighted Petersen grab (1/16 m2).
The Petersen grab was used three times at each site. The triangular dredge (about 1 m in width and 0.5 cm in mesh