In concrete affected by alkali–silica reaction (ASR), aggregates react in the high pH environment and cause deleterious expansion and cracking of the concrete. Leaching of alkali metals from the concrete might therefore locally reduce ASR. However, few data on alkali metals leaching are available in the literature. Our goal was to document the alkali metal leaching and to build-up an alkali inventory (the amount in solid and in solution, and the amount released by the aggregates) in a full-scale structure, the 50-year-old Votna I dam in Norway. Free alkali metal profiles were determined on cores taken at four locations with different exposure conditions: permanently immersed, periodically immersed, exposed to rain, or sheltered. Alkali leaching was observed at all four locations up to a depth of 100 mm. The leached zone exhibited less intense cracking than the non-leached concrete, indicating that the alkali leaching might be limiting ASR.