Sediment plays an important role in freshwater and marine biogeochemical cycles; however, too much sediment is known to have deleterious effects on ecosystem processes. In the Great Barrier Reef catchments, knowledge about the particle size of the sediment is important as it affects the distance sediment can be transported, the nutrients it carries and its ability to transform channel structure. This paper combines the results from recent research on fine sediment (<63 µm) and how it affects coral reef ecosystems, with some new OSL dating on coarse sediments (>63 µm) in the Fanning River basin. The integration of this information provides insights into the impact of land use change on sediment delivery in large tropical catchments. The results suggest that while the fine sediment may reach marine ecosystems over event time scales, the coarse material is having an impact closer to its original source, where it is altering channel structure and potentially impacting on local freshwater ecosystems.