Two kinds of 2-methylisoborneol-producing blue-green algae, Oscillatoria geminata and O. limnetica, and three kinds of geosmin-producing algae, O. amoena, O. splendida, and Aphanizomenon flos-aquae, were isolated from a park pond, a fish-cultivation pond, a river, and a reservoir. An oscillatorian species isolated from an air conditioning cooling tower was shown to yield both 2-methylisoborneol and geosmin simultaneously. Care was taken to ensure that the blue-green algae identified were those responsible for the musty odor compounds.