The objectives of this study were to quantify the amount of the stream discharge, nutrient fluxes, suspended sediment loss, and to define the relationship between streamflow and these parameters in a forest-covered watershed. The study was carried out in an experimental watershed, which has been monitored since 1979 in the Belgrad forest in Istanbul. Significant linear regressions were obtained between streamflow and discharge of selected water quality parameters. Mean monthly losses were 10.01 kg/ ha for HCO3-, 5.92 kg/ ha for CI-, 0.07 kg/ ha for total N, 1.29 kg/ ha for Mg2+, 3.59 kg/ ha for Ca2+, 2.59 kg/ ha for Na+, 1.82 kg/ ha for K+, 0.0113 kg/ ha for P-PO43-, and 35.82 kg/ ha for suspended sediments. Among the monitored water quality parameters, HCO3-, CI-, and Ca2+ had greater losses than the rest of the chemical parameters studied in the watershed. Net gains ( influx exceeded outflux) calculated for total N, Mg2+, K+, and P-PO43- in the annual basis can be considered as an addition to the ecosystem's organic nutrient pool. In contrast, net losses occurred for HCO3-, CI-, Ca2+, and Na+.