The surface waters of the Mackenzie River drainage basin, Canada are virtually unpolluted. A suite of 101 surface waters was collected mainly during a three week period in the summer of 1969 and represents an instant in time during a period of average flow for most rivers in the basin. Twenty two major and minor inorganic chemical components are reported, together with physical properties and documented details of the area and proportion of rock types in the sub-basins. Q-mode factor analysis demonstrates that three factors account, essentially equally, for nearly 96 per cent of the information among the samples. They represent the influence of solution of evaporites and associated carbonate rocks, the influence of weathering products of calcareous marine shales, and the influence of weathering products of igneous and metamorphic rocks and non-calcareous shales. R-mode factor analysis shows that over 91 per cent of the variance is accounted for by seven factors, summarized below: Factor Major (minor) loadings Source 1 Ca-Mg-Sr-HCO3-(SO4) Carbonate minerals and gypsum 2 K-B-(Na) Illite 3 SiO2 Bentonites and hot springs 4 PO4 (organic) Particulate organic matter 5 Fe-B-(Na) Glauconite 6 Na-Cl Halite 7 U-SO4 Uranyl-sulphate complexes The factor results confirm that the main control on the inorganic composition of these surface waters is exerted by the bedrock encountered by the water during its residence in the sub-basins. The Mackenzie River, where it enters the delta, has contents of Li(< 5 μg1.), B(20 μgg1.) and F(0.09 mgl.) which are close to suggested world average river composition, whereas the content of U(0.5 μg1.) is higher. Strontium (0.21 mg1.) is about four times the suggested world average, due mainly to abundant fossiliferous carbonate rocks, whereas SiO2(3.5 mg1.) is much less. The base metals Ni(< 2 μg1.), Cu(2 μgl.) and Zn(l μg1.) are present at levels about one order of magnitude lower than suggested world averages but, due to the analytical techniques used, our values represent near true soluble ions whereas the world averages may include some metals extracted from suspended material.