The Onkaparinga River is a significant coastal waterway flowing into Gulf St. Vincent near Adelaide, South Australia. It features a diverse estuary system transitioning from freshwater reaches upstream to a tidal river mouth, creating varied habitats that support a mix of estuarine and marine fish species. The river flows through the Onkaparinga River National Park and Onkaparinga River Recreation Park, offering protected natural areas for recreation. Fishing here is primarily an estuarine and saltwater pursuit, with the river's character and fish populations heavily influenced by tidal movements and seasonal patterns.