Environmental gradients and phytoplankton community were studied on a monthly basis, at 3 stations of Lake Yongdam, from April 2002 March 2004. During July to August, thermocline formed at the depth of about 10 m, but it was lowerd depth, in between 25${sim}$30 m in October. Monthly variations of the epilimnetic (0${sim}$5 m) TP concentrations at station 1, 2 and 3 were in the range of $5.1{sim}36.1;mg;P;{cdot};m^{-3}$, $6.1{sim}77.7;mg;P;{cdot};m^{-3}$ and $6.7{sim}47.7;mg;P;{cdot};m^{-3}$ respectively; with higher concentrations at the upstream areas showing. Monthly average of the epilimnetic (0${sim}$5 m) TN concentration at Station 1 was in the range of $0.88{sim}1.73;mg;N;{cdot};L^{-1}$, and Station 3 was in the range of $0.94{sim}2.77;mg;N;{cdot};L^{-1}$, which is higher if compared with the values of station 1. Transparency wa:s in the range of 0.8${sim}$6.7 m, with lower values at upstream areas and higher at the downstream area. As for phytoplankton, during the winter season, diatoms had high appearance rate; during the spring season, Cyclotella comta, Aulacoseira ambigua f. spiralis, A. granulata and similar diatoms, during spring and summer Ankistrodesmus spiralis, Chodatella subsala, Crucigenia irregularis, Coelastrum cambricum, Scenedesmus ecornis v. ecornis.