Although the precise route and mode of transmission of Helicobacter pylori are still unclear, molecular methods have been applied for the detection of H. pylori in environmental samples. In this study, we used the direct viable count fluorescent in situ hybridization (DVC-FISH) method to detect viable cells of H. pylori in the River Aliakmon, Greece. This is the longest river in Greece, and provides potable water in metropolitan areas. H. pylori showed positive detection for 23 out of 48 water samples (47.9%), while no seasonal variation was found and no correlation was observed between the presence of H. pylori and indicators of fecal contamination. Our findings strengthen the evidence that H. pylori is waterborne while its presence adds to the potential health hazards of the River Aliakmon.