The diets of lake resident and both allopatric and sympatric migratory (diadromous) forms of common smelt (Retropinna retropinna(Richardson)) in Lakes Waahi and Whangape (Lower Waikato River system, New Zealand) were examined before and after collapse of macrophyte beds and loss of associated invertebrates. Before this diets were varied, but dominated by chironomid larvae and pupae, supplemented by semiplanktonic crustaceans in small smelt in particular and by corixids in larger smelt. Afterwards diets were less diverse and the main food items were mysid shrimps. The opportunistic, generalist feeding habits of smelt help their survival of habitat changes.