Gammarus balcanius, the commonest amphipod species in the mountainous and submountainous areas of Romania, has been the subject of various approaches regarding the relation between the species distribution and water quality. This paper compares by means of the one-way ANOVA test the data collected from the sampling stations where this species was detected with the data from the sampling stations where the species was not detected. Several parameters were taken into account: altitude, pH, dissolved oxygen, chemical oxygen demand, hardness, anionic surfactants, tannin, lignin, cyanide, nitrate, nitrite, ammonia and soluble reactive phosphorus. The preference of the species for a high level of dissolved oxygen, the low level of chemical oxygen demand, nitrite and soluble reactive phosphorus were the statistically significant results. The low levels of ammonia and anionic surfactants and the result regarding altitude are also close to the margin for statistical significance. All these results point to the conclusion that the species under scrutiny prefers the clean waters of the mountain streams’ middle and superior segments.