The aim of the present work was to observe the morphological differences between bacteriophages from sewage, recent pollution and those from samples that contain microorganisms that have survived either natural inactivation or water treatment processes (persistent pollution). We studied the occurrence of bacteriophages infecting Bacteroides fragilis (HSP4O strain), F-specific coliphages (HS(pFamp)R strain) and somatic coliphages (CN13 strain). Phages isolated with B. fragilis in both wastewater and samples with persistent pollution were in all cases members of the Siphoviridae group with flexible tails. With E. coli strain HS(pFamp)R we detected F-specific coliphages in 97.7% wastewater. However, the percentage decreased to 76.9% in samples with persistent pollution. In the case of somatic coliphages in wastewater, detected using E. coli CN13, 91% of the phages belonged to the Myoviridae family and a 6% to the Siphoviridae family. In contrast, in persistent pollution samples, an increase of Siphoviridse phages was observed (up to 26.4%).