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Wetlands in the Mississippi River deltaic plain are deteriorating in part because levees and control structures starve them of sediment^,,. In spring 2011 a record-breaking flood brought discharge on the lower Mississippi River to dangerous levels, forcing managers to divert up to 3,500 m³ s⁻¹ of water to the Atchafalaya River Basin. Here we use field-calibrated satellite data to quantify differences in inundation and sediment-plume patterns between the Mississippi and Atchafalaya River. We assess the impact of these extreme outflows on wetland sedimentation, and use in situ data collected during the historic flood to characterize the Mississippi plume’s hydrodynamics and suspended sediment. We show that a focused, high-momentum jet emerged from the leveed Mississippi, and delivered sediment far offshore. In contrast, the plume from the Atchafalaya was more diffuse; diverted water inundated a large area …