This study aimed to investigate the presence and abundance of antibiotic resistance genes (ARGs) in bacterial and phage DNA fractions from sediment samples collected from the Onyar River, both before and after its passage through the urban area of Girona (northeast Spain). Genes conferring resistance to β-lactams, fluoroquinolones, macrolides, sulfonamides, and tetracyclines were quantified using quantitative PCR. Our findings showed that ARGs are present in both bacterial and phage DNA fractions, with a higher abundance in the bacterial fraction. Notably, our analysis revealed an increased abundance of the sulfonamide resistance gene sulI in the phage DNA fraction when comparing samples collected before and after the river's passage through the city. Although similar trends were observed for other ARGs (e.g., qnrS and sulII), these differences were not statistically significant (p > 0.05). These findings emphasize the importance of phages as potential reservoirs or vehicles for ARGs in environmental settings. Further research is needed to elucidate the factors that influence gene transfer dynamics and the persistence of ARGs within phages.