is widely known to be the etiological agent of the life-threatening diarrheal disease cholera. Cholera remains a major scourge in many developing countries, infecting hundreds of thousands every year. Remarkably, is a natural inhabitant of brackish riverine, estuarine, and coastal waters, and only a subset of strains are known to be pathogenic to humans. Recent studies have begun to uncover a very complex network of relationships between and other sea dwellers, and the mechanisms associated with the occurrence of seasonal epidemics in regions where cholera is endemic are beginning to be elucidated. Many of the factors required for the organism's survival and persistence in its natural environment have been revealed, as well as the ubiquitous presence of horizontal gene transfer in the emergence of pathogenic strains of . In this article, we will focus on the environmental stage of pathogenic and the interactions of the microorganism with other inhabitants of aquatic environments. We will discuss the impact that its environmental reservoirs have on disease transmission and the distinction between reservoirs of and the vectors that establish cholera as a zoonosis.