The entire area was covered by ice during the last glaciation, and the peatlands have accumulated over the last ten thousand years. Plants from more temperate regions mix with arctic species. A majority of the wetland is peat bog, although salt marshes occur along the coast, and marshes and wet meadows occur along the major rivers. The wetlands provide important habitat for migratory birds including shorebirds (e.g., yellow rail) and waterfowl (e.g., snow geese). Large mammals include polar bears and wolverines.