The marine resources of the Seaside Adjunct to Kejimkujlk National Park are contained within two large tidal lagoons located behind sand beach-dune complexes which partially isolate them from the sea. These systems, along with four small brackish-water headponds, have been described in terms of their origin, geology, physiography, morphology, sediment types and sedimentation processes, biology and input/output relationships. The major emphasis has been placed on identification and documentation of the biological habitats and communities present, and the factors responsible for their development and maintenance, with a view to making recommendations for monitoring, conservation, and preservation of these resources.

The major habitat types within the lagoon consists of high salinity coastal oceanic water, salt marshes, intertidal sand and mudflats and subtidal mudflats. The pelagic community is primarily oceanic in nature there being little freshwater input, relative to tidal exchange, to allow development of typically estuarine communities. Salt marsh habitats exist primarily on a narrow band along the shore zone, but occasionally occur on isolated islands on the higher intertidal flats and, where streams enter the lagoon, as larger meadows. Intertidal sand and mud habitats are poorly developed as a result of the unstability of substrates caused by high tidal current velocities and the coarse nature of sedimentary materials. The subtidal benthic community is dominated by eel grass beds located primarily in the upper reaches of the basins.

The physical factors associated with these habitats, particularly the high current velocities and resulting unstable substrates, leads to high community diversity but low species diversity and presents an extremely interesting environment for both interpretive and recreational activities.