Channel degradation can affect flow and inundation in alluvial rivers which may have negative geomorphic and ecological impacts. It is difficult to define and characterise channel degradation in low-energy, floodplain wetlands where channels vary in size, shape, and dominant hydrogeomorphic processes. Similarly, it is difficult to link channel erosion to other factors, such as ecological degradation in a river, which typically refers to a decline in structure, function, and/or resilience of aquatic and riparian ecosystems. This study examined geomorphic factors related to channel degradation in Gum Cowal, Macquarie Marshes. Gum Cowal is a reoccupied palaeochannel with a broad macro-channel hosting shallow lagoons and multiple reticulate thalwegs in its bed. The techniques used in the study included channel mapping, field surveys and cross-section analysis. Surface soil and vegetation parameters were measured at paired sites. Channels in the study area ranged from 8 to 20 m wide, and from 0.1 to 0.85 m deep. Degraded channels were deeper, had less vegetation ground cover, and showed evidence of incision (e.g. exposed tree roots) when compared to nearby intact channels. Degraded channels also had sandier, less cohesive topsoils than intact channels. It appears that a positive feedback occurs between channel erosion, loss of vegetative cover, exposure of dispersive subsoils, and reworking of sand from upstream to downstream. These findings are relevant to water, river, wetland, and agricultural management in semiarid landscapes, and for conservation and restoration of floodplain wetlands to maintain critical ecosystem services.