area of low, flat, poorly drained ground that is subject to daily or occasional flooding by salt water or brackish water and that is covered with a thick mat of grasses and such grasslike plants as sedges and rushes. Salt marshes are common along low seacoasts, inside barrier bars and beaches, in estuaries, and on deltas and are also extensive in deserts and other arid regions that are subject to occasional overflow by water containing a high content of salts. Maritime salt marshes often extend many miles inland and are variably subject to tidal action; inland brackish marshes are found frequently on mineral substrates of alluvial and lacustrine origin.