Our paper focuses on the characteristic of mammalian and bacterial viruses in aquatic environments. We described their role and occurrence in different types of environmental water. It is known that the role of viruses present in a water environment can be negative or positive. A negative role is connected with pathogenic viruses and positive with bacteriophages. Pathogenic viruses can cause diseases, whereas bacteriophages in water environment are an important component of the microbial loop in terms of their potential roles in regulating microbial mortality, production, community structure, and biochemical cycling.