Coastal river systems are highly complex and serve as important corridors for diadromous fish species that rely on habitats in both marine and freshwater environments to complete their lifecycles. Movement between these environments is important as it provides access to different habitats to optimise growth, survival and reproduction. In this study, we used acoustic telemetry to quantify the relative importance of abiotic stimuli in relation to seasonal movement patterns in blue salmon catfish, Neoarius graeffei throughout an unregulated coastal river catchment, the Clarence River in northern New South Wales, Australia. Thirty individuals were surgically implanted with acoustic coded tags and movements were recorded passively by a linear array of 32 acoustic receivers, encompassing approximately 164 km of river throughout the lower reaches of the Clarence River and selected tributaries. Movements were monitored over a period of approximately 12 months. We found that blue salmon catfish in the Clarence River catchment are mostly confined to lower Clarence reaches and move between the upper estuary to freshwater habitats well beyond the saltwater and freshwater interface. River flow was influential in N. graeffei seasonal movements with fish moving downstream in during high flow events. Our results provide a better understanding of the movement corridors that N.graeffei use in a coastal river at the southern extent of its range. Human impacts to coastal systems, particularly changes to the natural flow regime as a result of river regulation, have the potential to alter the movement patterns of species like N.graeffei, that use flow to cue their movements in unregulated coastal systems.