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Concentrations of dissolved silicon (DSi) in the ocean have the potential to impact the drawdown of atmospheric CO2 because diatoms, which account for 43% of marine primary productivity, have an absolute requirement for DSi. Rivers are the main source of Si to the oceans, and despite the importance of rivers to the marine Si budget and CO2 drawdown, the controls of river DSi flux are not fully resolved. To help understand the controls of river DSi export, we investigated the relationships between river DSi yield and various environmental parameters for watersheds in western Canada, including climate, land cover, lithology, slope, and soil. Statistical analyses indicated that land cover and climate are the best predictors of DSi yield in western Canada. The land cover classes with the highest correlation to DSi yield were mixed forest, savanna, and wetland. Our results indicate that future climate change and shifting vegetation distribution have the potential to impact DSi export from continents to oceans, which has implications for the marine Si budget and atmospheric CO2 drawdown.