Abstract:The trophic states of 18 drinking water supply reservoirs and the response of plankton were surveyed in Guangdong Province in 2000. Total nitrogen (TN), total phosphorus (TP) and Secchi disk depth (SD) varied from 0.15 to 7 15mg/L, 0 003 to 0 387mg/L and 0 4 to 6 3m, respectively. They all showed high correlation with chlorophyll a that varied between 0 6 and 32 3mg/m 3. Trophic state indexes (TSI) based on TN, TP, SD and chlorophyll a were between 23 7 and 55 1, without apparent seasonal variat...