Interactions of microbes common to water resources were investigated. Nematodes were able to distinguish between food bacteria and non-food bacteria, and between bacteria and lake bottom mud. They preferentially migrated to and fed on a Vibrio species at various distances, temperatures, and pH values. Migration to food bacteria increased with an increase in bacterial concentration. Resting and dead bacteria did not attract nematodes. Nematodes migrated to food bacteria even when they had to move into areas having reduced oxygen tensions or under a barrier to reach bacteria. Nematodes were not attracted by carbon dioxide. They did migrate, however, to a dialysate from food bacteria. Nematode predation resulted in greater reductions in viable numbers of bacteria than total numbers of bacteria. Interactions between bacteria and bacteriophage occurred under a variety of temperature and pH values. P. aeruginosa in the presence of its phage utilized oxygen at a greater rate than in the absence of phage. Nematodes were observed to disseminate bacteriophage over a surface seeded with host bacteria.