We investigated population size, nest success, and nest-site characteristics of Saltmarsh Sharp-tailed Sparrows (Ammodramus caudacutus) from 1993 to 1998 in a salt marsh near Galilee, Rhode Island. From 1956 to 1997, tidal flow was restricted in the marsh by construction of a road with small culverts, which resulted in conversion of the marsh from short- and tall-form cordgrass (Spartina alterniflora) and marsh hay (S. patens) to one dominated by >5 m tall common reed (Phragmites australis). In fall 1997, self-regulating tide gates were installed to restore the historic tidal regime and vegetation. We documented declines in adult sparrow population sizes (17–25% annual decline) and productivity (48% annual decline) while the tidal regime was restricted. Nest success was variable (10–83%) before 1998, with predators accounting for most nest losses. Saltmarsh Sharp-tailed Sparrows usually nested in marsh hay, short-form cordgrass, and short common reed. After restoration, sparrows nested where vegetation was taller, which permitted greater nest elevation. However, 91% of nests failed due to flooding following installation of new tide gates. We hypothesize that restoration efforts will have short-term negative impacts on Saltmarsh Sharp-tailed Sparrow populations until salt marsh habitats are restored in higher sections of the marsh.