Sometimes present in freshwater and brackish water fish and crustacean shellfish in both natural and farmed environments. The causative chemicals have been shown to be geosmin and 2-methylisoborneol released by microorganisms in the water. The chemicalsare taken up by the fish through their gills to induce the taint in the flesh. The two chemicals have extremely low detection thresholds, in the order of 1 nanog/l.