A pseudanabaena species from Castaic Lake, California, that produces 2-methylisoborneol

Castaic Lake, a large reservoir in Southern California, experienced a two-month episode of the musty-smelling compound 2-methylisoborneol (MIB) in the fall of 1993. MIB levels in the water column reached or exceeded 150 ng/l. A Pseudanabaena bloom coincided with the off-flavor event. Fourteen odorous strains of the cyanobacterium were isolated, and eight of them were analyzed by gas-chromatographic methods to verify the presence of MIB in culture. The concentrations of MIB in culture ranged from 36 to 445 μg/l. This is the first documented report, to our knowledge, of a major MIB episode in United States drinking water that was attributable to Pseudanabaena, an organism not generally recognized as a taste-and-odor producer.