Despite the perceived importance of floodplain inundation to the ecology of lowland rivers, there is limited understanding of the contribution that floodplains make to the main river channel during floods. We sampled zooplankton communities, chlorophyll-a and Dissolved Organic Carbon (DOC) within the main river channel of the River Murray immediately upstream of the Barmah-Millewa Forest and at two sites immediately downstream of the forest during two flood events in July and October of 2010. Results demonstrate that while the smaller flood event in July did not contribute substantially to an increase in the amount of carbon (kg day-1) derived from the floodplain entering the river channel, the much larger flood in October resulted in a increase in carbon in the form of zooplankton from 200 to 3,000 kg day-1; chlorophyll-a from 100 kg to 600 kg day-1 and DOC from 15,000 to 300,000 kg day-1. These results clearly demonstrate that larger floods resulting in floodplain waters returning to the river will provide important subsidies of terrestrially derived carbon. This carbon may then become available to be incorporated into riverine food webs and provide a potential a boost to riverine secondary production.