Swamps are wetlands where standing or gently moving water occurs seasonally or persists for long periods, leaving the subsurface continuously waterlogged. The water table may seasonally drop below the rooting zone of vegetation, creating aerated conditions at the surface. Swamps are nutrient-rich, productive sites. Vegetation may consist of dense coniferous or deciduous forest or tall shrub thickets. On the South Coast, swamps occur in a range of sizes, often associated with a high density of skunk cabbage, sedge species, red alder, western redcedar and other vegetation tolerant of saturated organic soils. Species such as Northern Red-legged Frog as often found in large intact swamp communities surrounded by contiguous forest communities. On the South Coast, red-listed swamp communities include: red alder / slough sedge [ black cottonwood ], red alder / skunk cabbage, Sitka willow - Pacific willow / skunk cabbage.