Foraminifera are unicellular protests that occupy all marine habitats, including coastal marshes. Their population compositions are well known in estuarine settings and they can be used as biological indicators of human-induced environmental change. This study reports results from our investigation of marsh foraminiferal assemblages in the Minas Basin, Nova Scotia, Canada and Plum Island, Massachusetts, USA. We collected shallow 1-2 m marsh cores adjacent to anthropogenic structures constructed during the past several hundred years. In Nova Scotia the construction of estuarine dikes by early Acadian farmers resulted in a dramatic change in the sediment type in the Minas Basin. We observe rich peat at the base of the cores and oxidized red mud in the uppermost core. Foraminiferal population compositions also record a dramatic shift from Trochammina-Miliammina dominated assemblages in the peat to Trochammina inflata and Jadammina polystoma domination and decreased numbers of Miliammina fusca in the oxidized muds at the top. We interpret this change in both sediment and microfossil compositions as a direct result of Acadian dike construction that restricted open marine interaction in the estuary. At Plum Island we collected cores on both sides of a causeway constructed in the 1930’s. Anthropogenic impact is less apparent as both the foraminiferal populations and peat content change little down core. This may reflect the shorter duration of marsh disturbance at this location. This study successfully showed that foraminifera are useful paleo-environmental indicators and that the construction of dikes in marsh habitats disrupts normal marsh foraminiferal assemblages.