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The geomorphology of the Casco Bay shoreline has a profound effect on the size, characteristics and spatial distribution of tidal marshes in the region. Casco Bay’s steep shorelines and narrow, glacial cut coastal embayments provide relatively few opportunities for development of extensive salt marshes. On the basis of area and frequency, tidal marshes in the region are dominated by wetlands that form in glacier‐cut coastal valleys. A smaller but still significant fraction of the tidal marsh area along the Casco Bay shorelines exists in a narrow, discontinuous ribbon of green perched between tidal waters and adjacent hillsides. This unique geomorphic setting means that lessons learned from evaluations elsewhere of vulnerability of tidal marshes to sea level rise provide limited insight into implications of sea level rise (SLR) for Casco Bay’s wetlands.