Fresh water swimming can lead to -

The highest burden of leptospirosis falls upon those at lower socioeconomic levels whose activities of daily living bring them into contact with surface waters contaminated with the urine of animals carrying the infection. High rates of endemic leptospirosis, associated with both mild and severe disease, are found throughout tropical regions. Torrential seasonal flooding in areas of high population density (e.g., in urban slums in Brazil, India, and Thailand) is the major risk factor for epidemic severe disease. The nymphal stage of the deer tick Ixodes scapularis is the primary vector for transmission of Babesia microti . Transmission occurs from May through September. The vectors for transmission of B. duncani and B. divergens -like organisms remain unknown. Babesiosis is occasionally acquired by transfusion of blood products, primarily packed RBCs; (Harrison's Principles of internal medicine, 20th edition)