The Suisun Marsh Salinity Control Gates (SMSCG) have the potential to increase low-salinity-zone habitat for endangered Delta Smelt (Hypomesus transpacificus, California Endangered Species Act listed as Endangered, Federal Endangered Species Act listed as Threatened), and to allow them to more frequently occupy Suisun Marsh, especially Montezuma Slough, one of their most important rearing habitats. Operation of the SMSCG in summer and fall to improve Delta Smelt habitat are called for in the Biological Opinion and Incidental Take permit for the Central Valley Project and State Water Project. To support the adaptive management of the action, the California Department of Water Resources monitored the change in water quality, phytoplankton, zooplankton, fishes, and clams resulting from the action in 2018. This data package includes data collected by the Interagency Ecological Program’s (IEP) long-term monitoring programs supplemented with targeted sample collection where existing surveys lack spatial or temporal coverage. This package also includes modeling the change in Delta Smelt habitat based on area of open water with appropriate temperature, salinity, and turbidity. Monitoring during no-action years (2019 and 2020) will be used as a baseline for comparison during action years. This data package will be updated annually during both action years and non-action years.