River suspended sediment plays an important role in the health of aquatic and coastal ecosystems. While river engineering (e.g., dam construction), land use and land cover change (LULCC), and climate change are widely recognized as the major drivers of suspended sediment in the Anthropocene, their relative contributions to river sediment changes in large regions are rarely quantified using Earth system models. Here, we use new capabilities for modeling the coupled land-river sediment dynamics in the Energy Exascale Earth System Model (E3SM) to investigate the historical and future changes of suspended sediment in four coastal watersheds of the U.S. Mid-Atlantic, including the Susquehanna River, Potomac River, James River, and Delaware River, which are the major rivers draining to Chesapeake Bay and Delaware Bay. We find that in the last century dam construction and LULCC jointly drove the changes of suspended sediment in the heavily regulated Susquehanna River, whereas LULCC was the dominant driver in the other rivers. We also show that suspended sediment concentrations vary by at least threefold of magnitude along the channels of the Mid-Atlantic rivers and have been in decline since 1901 due to reservoir trapping and reforestation. As a result, river reaches with high turbidity, once a concern among residents in the region, have almost disappeared. We project that climate change and dam decommissioning will not imperil the improvement of water clarity in rivers of the U.S. Mid-Atlantic in the 21st century.