This study has been made for the purpose of investigating pH value, water temperature, dissolved oxygen, photo-intensity, transparency and vertical distribution of plankton during the spring-time from March to June, in 1968 at Uiam, Chunchon, and Paro Reservoirs. The results obtained from this study are as follows: 1) The clinolimnion ranged from 26.5℃ to 8℃ of water temperature was apparently appeared and the vertical distribution of water temperature had its marked thermocline in the 10-20m layer at Paro Reservoir, but these phenomena did not appear at other reservoirs. 2) Value of pH, dissolved oxygen are similiar at three stations and no thermal stratification was found. 3) The grade of transparency was the depth of 3.5m in all the reservoirs, and striking difference of transparency did not appear at all stations. The photo-intensity of 24m appeared at Chunchon and Paro reservoirs, but 6.8m at Uiam. 4) The total number of plankton samples collected at the three stations were identified and classified 52 species and the number of phytoplankton and zooplankton of them identified was 34, 18 species, respectively. The highest percentage of plankton species existed in Chunchon Reservoir.