Abstract - The Columbia River estuary serves as an important migration, rearing, and transition environment for juvenile anadromous salmon before they enter the sea. Historical modifications to the estuary, including diking of peripheral wetland and floodplain habitats and regulation of river flows by dams, have reduced salmonid access to shallow rearing habitats and may have eliminated sources of macrodetritus that fuel the estuary's food webs. Although there is emerging evidence that these estuarine changes are limiting juvenile salmon production and life history diversity, lack of information about historic and modern habitat conditions in the estuary, or the ecological consequences of habitat change, undermine existing salmon recovery efforts of the Columbia Basin Fish and Wildlife Program. This proposal addresses specific information needs identified in a recent interdisciplinary assessment of the hydroelectric system's impacts on estuarine habitat conditions for juvenile salmon. The primary elements of this proposal include: (1) retrospective analyses to reconstruct historic bathymetric features and assess effects of climate and river flow on the extent and distribution of shallow water, wetland and tidal-floodplain habitats; (2) computer simulations using a 3-dimensional numerical model to evaluate the sensitivity of salmon rearing opportunities to various historical modifications affecting the estuary (including channel changes, flow regulation, and diking of tidal wetlands and floodplains); and (3) life-history specific information based on present and historic food web sources as determined by stable isotope, microchemistry, and parasitology techniques. From these data and additional modeling simulations that will be selected during an estuarine habitat restoration workshop, we will (4) examine effects of alternative flow-management and habitat-recovery scenarios on habitat opportunity and the estuary's productive capacity for juvenile salmon. This project is collaborative with NOAA and other partners; this contract primarily covers work on elements 2 and 4.