Between October 1999 and April 2000, we surveyed the waterbirds at Lake Lashihai, China. A total of 52 species were recorded, of which one species was a resident, 34 were winter visitors, and 17 were passage migrants. Species richness was highest in November. Passage migrants mainly occurred in October, November, and April, and they stayed longer at the lake during their autumn migration than during the spring migration. The seasonal distribution pattern of total numbers of all waterbirds was bimodal. One peak occurred between late December and early January, and the other in middle March. The seasonal distribution patterns of 15 common species have been classified as bimodal, unimodal, or irregular. The numbers of five common species were variable in middle winter, and their numerical change in contiguous weeks were more than 30%, suggesting that local movements might be frequent.