Abstract: This article explores recent developments along the Mississippi River Ship Channel, the Mississippi River Delta, and the port city territory of New Orleans, US. The lower reaches of the Mississippi River through which the ship channel is maintained have become increasingly porous over the past decade, as flooding events have triggered or expanded multiple breaches or crevasses along the river’s eastern bank. This increasing porosity has generated debates between political and economic assemblages favoring different approaches to navigation management, flood control, and ecosystem restoration. The tensions and contradictions facing delta residents, planners, managers, and engineers come down to a question of hydrological porosity in the Mississippi River Delta, both in the river’s navigation channel itself, but also in the estuarine basins that extend from its banks towards the Gulf of Mexico. This article describes how over the past several decades different modes of porosityhave emerged in scientific and public discourse around water management. The science and politics of these competing modes of porosity animate a great deal of environmental decision-making in the region today. The article’s analytical framework bridges research focused on the theme of porosity in port city territories, the political ecology of infrastructure standards, and management pathologies in ecosystem management.