Based on analyzing the hydrochemical and hydrobiological indicators, a characterization is provided for the water-ecological situation on the territory of the location area of the Vostochnyi Cosmodrome (Amur oblast). An assessment is made of the consequences of the influence exerted by the processes of constructing the Cosmodrome facilities on the ecosystems of the streams used in the study. The streams that were investigated in June–July 2014 are distinguished by a low mineralization of water, and by a neutral or weakly alkaline reaction of the medium. In most of the small streams, the content of mineral forms of nitrogen and total phosphorus corresponded to clean waters, whereas large rivers showed increased content levels of nitrates and ammonium. The content of most trace elements in the water is extremely low, and significant concentrations were observed in some streams for iron and manganese only. The streams are noteworthy for high taxonomic diversity of hydrobionts. The investigations recorded 106 algal species of phytoplankton and 153 species of phytoperiphyton and phytobenthos, and 38, 60 and 108 species of macrophytes, zooplankton and zoobenthos, respectively. A general analysis of results from field investigations showed that the present water-ecological situation in the location area of the Vostochnyi Cosmodrome under construction can be categorized as “relatively satisfactory”. The study did not reveal any negative consequences of the influence exerted by the processes of constructing the Cosmodrome facilities on the ecosystems of the streams in the area under investigation. According to the hydrological, hydrochemical and hydrobiological characteristics, the streams within the Zeya river basin are typical small and moderate-size streams. A significant hydraulicity of the streams, caused by the specific character of the monsoon climate, and also high oxygen content levels and the absence of pollution with organic matter and heavy metals create favorable conditions for physical and chemical self-purification.Keywords: small and moderate-size streams, rivers, Zeya, aquatic ecosystems, Cosmodrome, surface water quality.