Diatoms were identified and counted in a core of 78 cm long, from which eight phases were recognized.In 1596-1636, 1696.1836 and 1876-1946,Daihai Lake supported an Epithemia/Cymbella assemblage, indicating a shallow water environment.In the two intervals of the three periods mentioned above (1666-1696 and 1836-1876), occurred a Melosira islandica/Fragilaria assemblage comparable to that in modern arctic and glacial moraine lakes.This is surely attributed to the heyday and the last oscillation of the Little Ice Age.During 1636-1666 and 1946-1966, the diatoms were too rare to be counted.Since 1966.the lake has been dominated by Melosira granulata/var.angustissimas Diplanets elliptica and Fragilaria spp.This may be due to the slightly riiesotrophic water, the warmer climate and the disturbance of human beings.