The diet of the Imperial Shag (Phalacrocorax atriceps) at Vintter Lake, Patagonia, Argentina, was investigated through analysis of 157 regurgitate pellets collected during the summer seasons of 2008–2010 and 2016–2017. The native fish Galaxias platei was the main prey throughout the study period, accompanied only by a few gastropod species (2010) and coleopterans (2009 and 2016). Our results markedly differ from those previously reported for Imperial shags breeding at Vintter Lake and other sites. The results are discussed in relation to the population decline observed in shags at Vintter Lake throughout the study period.