Previous studies have correlated interannual streamflow fluctuations with changes in the climate. We note that decadal shifts in climate forcing can impart a stronger signal on streamflow than does the long-term climatic trend. In north-western North America, the Pacific Decadal Oscillation (PDO), which is strong in the cold season, may exert influence on interannual variations in spring high flows. In the 20th century, several major shifts in the PDO have been recognized. However, the rivers of Alaska, Yukon, Northwest Territories, British Columbia and Alberta have variable response to such climate signals. An analysis of the flow of rivers in this region indicates that a number of rivers draining the Pacific coast are positively correlated with PDO and some rivers in the interior correlate negatively. Not all river flows correlate with the PDO because factors such as location, topography and storage can overwhelm the climatic influence. Given these considerations, the interpretation of long-term trends in streamflow should take account of the interdecadal climatic shifts and basin characteristics that affect flow generation.