Granuloma, swimming pool: Localized nodular skin inflammation (small reddish raised areas of skin) caused by a bacterium called Mycobacterium marinum. Swimming pool granuloma is typically acquired by occupational or recreational exposure to salt or fresh water, often resulting from minor trauma during caring for aquariums. The diagnosis is suggested by the history of exposure and confirmed by culturing tissue specimens which yield the microscopic organism, Mycobacterium marinum. The infection can be treated with a variety of antibiotics. Also called "fish bowl granuloma."