Since the 1930s, combined streamflow from the largest Eurasian rivers discharging to the Arctic Ocean has been increasing. For many of these rivers, an increase in annual streamflow volume has been accompanied by a shift in seasonality (e.g., earlier snowmelt runoff in the spring). These changes in annual and seasonal streamflow may be due to direct effects of climate change (e.g., increased precipitation, or changes in snow accumulation and ablation patterns), indirect effects of climate change (e.g., changes in permafrost), or human effects (e.g., storage and release of river runoff in reservoirs). We develop and describe a method to estimate the potential contributions of artificial reservoirs to long-term changes in annual and seasonal streamflow between 1937 and 1998. Reservoir effects on downstream flow are simulated using a reservoir routing model coupled off-line to the Variable Infiltration Capacity (VIC) land surface hydrology model for the Lena, Yenisei and Ob' river basins. The effects of reservoirs on basin average evaporation are also represented. We perform trend analysis on long-term (≥30 years) time series of seasonal and annual streamflow and isolate the effects of reservoirs. Although reservoirs have had little effect on trends in annual discharge from the Lena, Yenisei, and Ob' river basins, we conclude that they are responsible for many of the seasonal changes that have been observed. For the Lena, reservoirs account for up to 80% and 30% of the observed winter and spring trends, respectively. For the Yenisei, reservoirs account for up to 100%, 40%, and 60% to 100% of the observed winter, spring, and late summer to early fall trends, respectively. For the Ob', reservoirs may account for more than 70% of the observed trends during the months of January to March. A result of this study is a set of reconstructed streamflow at the outlets of the Lena, Yenisei, and Ob' river basins which can be used in subsequent studies to improve the understanding of climate change effects on runoff generation in the Eurasian Arctic.