Norovirus (NoV) is one of the most common causative agents of waterborne gastroenteritis outbreaks. The main objective of the study was to determine the presence of human NoVs in river water and in treated wastewater (TW) released into the river. During a one-year survey in 2007/2008, NoVs were detected in 30.8% of river samples (20/65), and 40.5% of TW samples (17/45) with a real-time reverse transcription-PCR assay. NoVs were present in the river water in the winter and spring, coinciding with the NoV epidemiological peak in the community and the presence of NoVs in TW. Later in 2009, the concentration method used, pre-filtration with a Waterra filter combined with filtration through a negatively charged membrane, was evaluated against glass wool filtration and freeze-drying for the detection of adenoviruses in river water. The virus amounts measured varied greatly depending on the virus concentration method. The continued monitoring in the spring of 2009 also revealed that the average concentration of noro- and adenoviruses in TW was 2.64 × 103 and 1.29 × 104 pcr units per mL, respectively. No correlation between the presence of viruses and Escherichia coli was found. These results may be useful for risk assessment studies.