Cyanobacteria blooms in drinking water sources are problematic as they can produce toxic secondary metabolites. The hepatotoxic microcystins, the most common algal toxins worldwide, are produced by many species of cyanobacteria. Conventional water treatment processes consisting of coagulation, flocculation, sedimentation and filtration do not remove these compounds, but if their occurrence in source water is sporadic, powdered activated carbon (PAC) can be a cost-effective option as it is applied only when required. The success of PAC depends on the application of a sufficient dose which will be determined by water treatment plant (WTP) conditions (flow rate), concentration of microcystin and the water quality of the source water, particularly the natural organic matter (NOM) concentration and character. Currently there is no information in the literature describing how changes in NOM affect the adsorption of microcystins onto PAC. In this study the adsorption of microcystin-LR (mLR) and microcystin-LA (mLA) onto a chemically activated wood based PAC was examined in a range of waters of varying NOM concentration and character. The dissolved organic carbon concentration (DOC) indicates the amount of NOM present while UV absorbance at 254 nm, color, SUVA (ratio of UV absorbance at 254 nm to DOC) and specific color (color to DOC ratio) give an insight into the character of the NOM. SUVA and specific color relate to the structure of the NOM regarding aromaticity and conjugation of double bonds. Includes table, figures.