Galchi reservoir situated in Daeami is believed to be polluted mainly by livestock production wastewater, which has been discharged from more than 12 small-scale dairy farms and eventually drains into the reservoir. Averaged field data of organic pollutants, nutrient salts and bacterial density taken at six sample sites were analyzed along downstream to explore the impact of wastewtaer on the pollution of water stream in a Daeami hilly region during August-November, 1996 (6 trials). The peak loading rates of pollutants (BOD_5, COD_(cr), and SS) of 95.1㎎/ℓ, 180.0㎎/ℓ and 40.0㎎/ℓ respectively, were observed at the spot where the main stream received wastewater effluent from dairy farms (sample site 3). The pollutant concentrations were 10∼40 times Beater than those at sample site 2, immediately upstream of this tributary. Higher concentrations of ammonium nitrogen (NH₄^+-N), nitrate nitrogen (NO₃^--N), and phosphate-phosphorus (PO₄^(3-)-P) of 20.37㎎/ℓ, 0.82㎎/ℓ and 0.59㎎/ℓ, respectively, were also observed at sample site 3. The concentrations of nutrient salts were 3∼4 times Beater than those at the site 2. The primary cause of the sudden increase of the organic pollutants and nutrient salts can be attributed to the intrusion of untreated livestock production wastewater into the main stream, which is eventually believed to pollute the Galchi reservoir. The correlation of indicating bacteria (total coliform group, fecal coliform group, fecal steptococcus) and organic matters (BOD_5, COD_(cr)) were investigated to determine the effects of oragnic pollutants on the microbial matrix in the stream. Good correlations existed between the organic pollutants, BOD_5, COD_(cr) and T-N and microbes(TC, FC, and FS)(R²∼＝0.5∼0.75). There was a fair correlation of T-P with microbes (R²∼＝0.45∼0.55). A similar result can be drawn from the correlations of nutrient salts, NH₄^+-N, NO₃^--N, and PO₄^(3-)-P and the microbes. The sedimentation of SS with downstream flow may lead to comparatively lower correlation than that of COD_(cr) and NH₄^+-N. The ratio of FC/FS (fecal coliform/fecal streptococcus), referred to as an indicator of the presence of dairy manure in water, was 1.3 at the sample site 3, which was a bit higher than the threshhold value of 0.7 suggested by Clausen et al. (1977). The inclusion of some domestic sewage with the livestock production wastewater effluent at sample site 3 may raise the ratio, which is still well below the municipal sewage value of 4.0. The FC/FS ratio strongly suggests that livestock production wastewaster is the source of pollutants in the main stream. Appropriate treatment of dairy manure is necessary to restore the functions of the Galchi reservoir for fishing, boating, and irrigation of paddy field.