A study on the water pollution of Gumho river by the relationship between physio-chemical conditions and water quality level by phytoplankton was examined at 6 sampling positions during the period from April 21 to August 11, 1982. Examination of physio-chemical water analysis such as temperature, pH, DO, BOD and biological analysis has shown 1. The average for Gumho river was 6.2 - 7.2 of pH, 2.6 - 9.4 mg/l of DO, 28.8 - 122.4 mg/l of BOD. 2. The phytoplankton identification in this survey period showed, Cyanophyceae is 7 genera 13 species, Bacillariophyceae 11 genera 32 species and Chlorophyceae 17 genera 27 species. 3. The results of biological water analysis were as follows: Banyawol was from oligosaprobic to $eta$-mesosaprobic. Dongchon and Gumdan was from $alpha$-mesosaprobic to $eta$-mesosaprobic, 3rd gongdan was from oemesosaprobic to $eta$-polysaprobic, Paldal was $eta$-polysaprobic and Gangchang was repolysaprobic. 4. To appear dominant algae there were Microcycstis, Oscillatoria, Anabaena, Melosira, Nitzschia and Synedra.