Beach seines, gill nets and otter trawls were used during 1979–81 to sample extensively the fish fauna of the Peel-Harvey estuarine system. Approximately 145,000 individuals were caught, representing 29 familes and 55 species. The Clupeidae, Teraponidae, Mugilidae, Apogonidae, Atherinidae and Gerreidae were the dominant families, each contributing at least 8.9% to the total catch and together contributing 86.2%. Seasonal catch data and length-frequency distributions were used to help clarify the way in which the estuary was utilised by fish. Nine of the 15 most abundant fish species were marine species which entered the estuary for variable periods while the other six were represented by populations in which the individuals were capable of passing through the whole of their life cycle within the estuary. In order of abundance, the nine marine species were Hyperlophus vittatus, Pelates sexlineatus, Aldrichetta forsteri, Mugil cephalus, Torquigener pleurogramma, Favonigobius lateralis, Pranesus ogilbyi, Gymnapistes marmoratus and Sillago schomburgkii, while the six species with estuarine populations were Apogon rueppellii, Atherinosoma elongata, Nematalosa vlaminghi. Atherinosoma wallacei, Cnidoglanis macrocephalus and Amniataba caudavittatus. The extent and seasonality of the distribution of the species within the estuary and associated river systems varied considerably. Evidence is also presented to show that fish tend to move further away from the shallow banks near the shore with increasing age and size. The fish fauna of the Peel-Harvey is compared with those of Cockburn Sound and the estuaries of the Swan-Avon and Blackwood rivers in Western Australia and with Botany Bay in eastern Australia.