Because of the fundamental biological investigations and also of the practical importance, the authors investigated interstitial subterranean water (hyporheic) near a polluted river Sava in the plain where the underground waters are considered as potable. With the comparison of the physical, chemical, bacteriological, saprobiological and faunistic characteristics of the river and its hyporheic zone in different seasons their mutual relation is detected. The results show the influence of polluted river water on the hyporheic water within the river bed to at least 2 m depth.