In some, the water flows out again. In others, there is no outflow so the water becomes very salty as evaporation concentrates minerals in the water. Mangroves form at the border between fresh and seawater and have a very large variety of specialists. See our page on the fascinating mangrove habitat and its occupants. Bogs are wetlands with accumulating peat formed because decomposition is slow.
Fens also produce peat but are fed by streams or by ground water.
Both are constantly wet. Because of the build up of organic matter, water in bogs is highly acidic. Carnivorous plants are often found in such habitats because they need nutrient supplements not available in the acidic soil. Temporary freshwater habitats may appear seasonally in otherwise dry areas, due to seasonal rains or changes in the water table. Because these pools are too shallow and seasonal to support fish, they are important breeding areas for amphibians and insects.