Understanding the relative contributions of different spawning habitats to adult fish populations is central to effective fisheries management and species conservation. The Tarek (Alburnus tarichi) is an adfluvial cyprinid that is endemic to the alkaline-saline waters of Lake Van, Turkey. Tarek are culturally and economically important to the region, and also threatened by anthropogenic impacts, including poaching, dams, water diversions, pollution, and habitat degradation. Here we analyzed otoliths from 120 adult fish caught in Lake Van in 2016-2017 to reconstruct the age structure and natal origins of this Tarek population. Ages ranged from 2 to 10 years, with most fish belonging to the 2011-2014 cohorts (age 3-5). We analyzed strontium isotope ratios from water samples collected in 2016 and 2018 to build a baseline map and then used linear discriminant function analysis to classify Tarek to their likely natal origins. We found that adult Tarek originated from at least 7 different major tributaries of Lake Van, with a majority of fish originating from the Gevas and Engil tributaries in the south. Furthermore, the relative contributions of fish from each tributary varied among years, suggesting that a mosaic of natal habitats may be important for population stability. These results suggest that protection of all Lake Van watersheds from anthropogenic disturbance could be valuable for maintaining the stability of the Lake Van Tarek population and fishery.