The observation data from stations near the Liujiaxia and Longyangxia reservoirs before some earthquakes are analyzed. It is shown that if earthquake observation points near the reser- voir or natural lake, the precursory phenomena are more prominent. In this paper, the possible mechanism of this phenomena is discussed. It is indicated that we can use the stations near reservoir and natural lake to predict earthquake near the lake or in a large area for short-imminent term.