Geosmin synthase (geoA) is the key biosynthetic gene responsible for producing the taste and odor compound, geosmin. In this study, environmental triggers behind geosmin production in nine reservoirs across Wales, U.K. were investigated between July 2019 – August 2020, whereby the abundance of geoA was quantified through quantitative Polymerase Chain Reaction (qPCR). Monthly changes in geoA against geosmin concentrations revealed geoA to be an indicator of geosmin concentrations, but only when geosmin concentrations exceeded 100 ng/L. Model analysis of a reservoir that experienced elevated geosmin concentrations, revealed nutrient ratios to be a better predictor of geoA abundance.