Carolina bays are elliptical depressions concentrated along the Atlantic seaboard within coastal Delaware, Maryland, New Jersey, North Carolina, South Carolina, Virginia, Georgia, and northcentral Florida. In Maryland, they are called Maryland basins. Other landform depressions, not widely accepted as Carolina bays, are found within the northern Gulf of Mexico coastal plain within southeast Mississippi and Alabama where they are known as either Grady ponds or Citronelle ponds. Carolina bays vary in size from one to several thousand acres. About 500,000 of them are present in the classic area of the Atlantic Coastal Plain, often in groups with each bay invariably aligned in a northwest-southeast direction. The bays have many different vegetative structures, based on the depression depth, size, hydrology, and subsurface. Many are marshy; a few of the larger ones are lakes; 36 square km Lake Waccamaw is an undrained one. Some bays are predominantly open water with large scattered pond cypress, while others are composed of thick, shrubby areas, with vegetation growing on floating peat mats.