Perhaps the most striking feature of the park is its sand dune system, which sits on a broken series of barrier islands extending over 25 kilometres. The dune system shelters the estuarine lagoons and salt marshes, forming a dynamic coastal environment greatly influenced by the presence of the Gulf of St. Lawrence. The dune system is intensively dynamic – changing with rising sea levels, storms, and the long-shore transport of sands.

Sloping gently to the coast, Kouchibouguac National Park is generally flat with small knolls separating river basins. The park’s large rivers, the Kouchibouguac and the Kouchibouguacis, depending upon tides, can be influenced by marine waters along their entire length within the park. Salt marshes fringe much of the low-lying protected shoreline of the estuarine lagoon system and provide important habitat for many aquatic species.