Salt marshes are productive ecosystems that provide critical breeding and foraging habitat for many bird species. Open marsh water management (OMWM), a method of mosquito abatement through habitat alteration, is a widely practiced management technique in Mid-Atlantic salt marshes. Although OMWM may alleviate the need for pesticide applications, the effect of these habitat modifications on obligate salt marsh breeding birds is not fully understood and remains an information priority for the United States Fish & Wildlife Service National Wildlife Refuge System. My objectives were to; (1) develop a method to quantify OMWM, (2) use an index of marsh bird community integrity to evaluate the effect of OMWM, and (3) determine the impacts of OMWM on Seaside Sparrow reproductive success and nesting ecology. I searched for and monitored nesting birds, performed callback and passive surveys, and estimated vegetation cover on 19 plots (1-3ha) within tidal marshes in Sussex County, Delaware in May-August 2006-2007. I categorized plots as limited (n = 10) or extensive OMWM (n = 9) based on the level of OMWM manipulations. I detected 29 species across all surveyed plots, but detected no difference in species richness between limited and extensive OMWM (P = 0.145). I defined four avian guilds: salt marsh obligates, wetland generalists, shorebirds, and gulls/terns to compare avian communities between limited and extensive OMWM. Only the relative abundance of the salt marsh obligate guild differed between limited and extensive OMWM and was more than 1.5 greater on limited OMWM sites than extensive sites (P = 0.015). Relative abundance of Seaside Sparrows was 2.5 times greater on limited OMWM than on extensive OMWM (P = 0.002). Seaside Sparrow territory density ( P = 0.002) and nesting density (P = 0.031) was also 2 times greater on limited OMWM plots than extensive OMWM plots. Nest survival rates were similar (P = 0.584). However, when comparing measures of productivity between limited and extensive OMWM, I found the number of Seaside Sparrow eggs/ha (P = 0.026) and fledglings/ha ( P = 0.053) were greater on limited OMWM plots. Seaside Sparrow nest survival rates did not differ between levels of OMWM, but reproductive output was greater on areas with limited OMWM. OMWM does not appear to benefit most marsh bird species or guilds, but may negatively impact populations of salt marsh obligate species and Seaside Sparrows. OMWM may be used as an alternative means of mosquito control, but should not be considered a method of habitat enhancement for obligate salt marsh bird species. Refuges concerned with protecting populations of Seaside Sparrows or other salt marsh obligate birds should limit amounts OMWM in high breeding areas.