High concentrations of coliphages were isolated during December and March when the maximum average daytime temperature reaches 20°C. Eight coliphages capable of infecting various strains of E. coli and a few selected members of Enterobacteriaceae were isolated. Although all polyvalent phages contained DNA, they showed variation in plaque size and heat sensitivity. These polyvalent phages may be exploited as a possible biological control of overwhelming populations of the coliforms and faecal coliforms in raw sewage prior to treatment.