The abundances of somatic coliphages, F-specific phages and B. fragilis phages were measured in freshwater environments with different levels of faecal pollution. In samples with recent pollution of domestic origin the numbers of the three groups of phages were highly correlated. In this set of samples B. fragilis phages were significantly outnumbered by F-specific and these by somatic coliphages. In waters with intermediate levels of pollution, coliphages were more abundant than phages infecting B. fragilis. The levels of the three groups of phages, which were very low, were similar in waters with persistent faecal pollution indicating that B. fragilis phages were most resistant to natural inactivation processes.

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