The Usturoi Valley (Basin area = 11.7km2, Length = 5.5km, Average altitude = 458m) is located in the southern region of the Guai Mountains. The nature of the substrate is stony and it is generally made of gravel and sand. The riverbanks are covered with forest vegetation The macrozoobenthic bioindicators colonize the aquatic environment substratum and they respond according to their tolerance degree to the pressures which influence water quality or aquatic habitats, thus reflecting the conditions in which they live. Following the macrozoobenthic samples, seasonally yielded during 2016-2017 in Usturoi Valley, it was found that the dominant groups were sensitive or with medium tolerance against pollution, and they were represented by: Amphipoda (33.97%) Ephemeroptera (24.40%) and Chironomidae (20.19%), Trichoptera (10.72%), Plecoptera (3.83%), Oligochaetes(3.73%) other Diptera (2.30%) , Hirudinea (0.29%), Coleoptera, Odonata and Decapoda (0.19%). The oxygen regimen, the nutrients regimen and the saprobic index reveal good quality water in the superior sector (the first quality class), respectively moderate quality for the middle sector (the 3rd quality class)
