The diet of the grey mullet (Mugil cephalusL.) was studied in Lake Waahi, and the Waikato River at Huntly —2 highly productive freshwater habitats in New Zealand. Grey mullet fed all year despite temperatures ranging from 7–26°C. Their diet was found to include a wide range of algal species, some macrophyte detritus, inorganic particles, and occasionally the snailPotamopyrgus antipodarum.The food items selected reflected their availability in the 2 habitats. The source of these food items is discussed and the environmental effects of mullet feeding activities are considered briefly.