This review aims at the presentation of rare, sporadic infection in animals and humans, following contact with contaminated water. Pythiosis, caused by a water mould Pythium insidiosum, occurs primarily in dogs, horses and humans, but can also affect calves, sheep, cats, birds and even panthers and tigers. Susceptible hosts become infected after contact with motile zoospores, that invade the wounded skin when the animals wade in stagnant water containing this opportunistic organism. In dogs, pythiosis affects the gastrointestinal system and lymph nodes, and seldom the skin. The clinical symptoms include vomiting, weight loss, intermittent diarrhea and palpable masses in the abdomen. Expansion of the infection to the pancreas, mesenteric lymph nodes and bile ducts can occur. Extensive weight loss may be evident. Cutaneous pythiosis is the usual presentation in horses. Skin lesions are pyogranulomatous or fibrogranulomatous and tend to be progressive. In the horse the lesions are large (up to 45 cm), discharging swellings, usually on the extremities, ventral trunk or head. Yellow, necrotic masses termed “kunkers” or “leeches” can be removed intact from the granulomas. Nasal mucosa can be involved. The respiratory condition caused by inhalation of aerosolized Pythium spores is a Pythium-induced allergic syndrome. In humans, three forms of pythiosis are observed: granulomatous and ulcerative lesions involving the skin and subcutaneous tissues of the limbs and face, ophthalmic pythiosis causing keratitis, and systemic pythiosis with vascular involvement leading to vasculitis, thrombosis and aneurysms.