From June 1991 to November 1992, biological and physio-chemical environmental factors were investigated 18 times at 5 stations in the upper area of Daechung reservoir. The ranges of heterotrophic bacteria were 2.5×10 exp (2)∼7.3×10 exp (4), proteolytic bacteria were 1∼6.7×10 exp (3), lipolytic bacteria were 0.6×10 exp (2)∼1.9×10 exp (4), spore forming bacteria were 2∼55(CFU/㎖), total coliform bacteria were ND∼1.1×10 exp (3) and fecal coliform bacteria were ND∼2.9×10 exp (2) (MPN/100㎖)during the investigated period. All bacterial distribution of station 1 was affected by the precipitation and the bacterial distribution of stations located on downstream it was affected by the water temperature instead of the precipitation. On the total result, monthly variation of bacterial distribution was stronger than stational variation, therefore the important environmental factor affecting to the distribution of bacteria was analysed as water temperature.