Human waste is a global concern, and volumes are growing rapidly. For opportunistic species, like many birds, urban waste offers alternative food which in turn may lead to plastic ingestion with potential negative effects. We assessed the incidence of plastics and other marine debris in breeding Kelp Gull (Larus dominicanus) diet at nine colonies located along ~2400 km of coastline from southern Buenos Aires to southern Chubut, Argentina, using regurgitated pellets (n = 2355) and chick stomach content samples (n = 588). Plastics were recorded at all colonies, and incidence varied between 0.0 and 16.2% in adult pellets and 0.0-12.5% in chick stomach content samples, depending on the colony, breeding stage and year. Contrary to our expectation, incidence of debris including plastics in Kelp Gull diet was relatively low despite its opportunistic feeding habits and widespread use of refuse dumps, even at colonies located close (<10 km) to these anthropogenic food subsidies.