From the Amazon and the Brahmaputra to Russia's Lena, Brazil's Negro, or South America's Paraná River, many of the world's largest rivers share a number of important characteristics: They are long, they are wide, they carry high volumes of water down a course with a shallow slope, and their flows are broken up by sand bars and small islands. Despite these broad similarities, sediment dynamics related to the formation of sand bars and islands in large, branching rivers can vary markedly from one to the next. A number of processes affect the formation and stability of midstream islands, such as the rate of riverbank erosion, the hydrologic regime (the long-term variability of the river's flows), and the colonization and growth rates of stabilizing vegetation. Although researchers have previously used reduced-complexity models to study river island dynamics, Nicholas et al. describe a new physics-based, two-dimensional morphodynamic model that realistically simulates branching river dynamics over large distances and long time scales.