TwoNostoc muscorum cyanophages were isolated from a domestic sewage in Kuwait. N-1L cyanophage had a hexagonal head with a long tail, while N-2S cyanophage was a short-tailed virus. N-1L cyanophage was active at 50°C and at acidic pH, compared with N-2S, which was more heat stable and active at pH 7.0. Seasonal variations in the total number of plaque-forming units ofN. muscorum cyanophages were determined for sewage samples collected at each treatment step.