Naturally occurring wetlands form when rain and runoff from watersheds saturate the ground or there is a continual flow of groundwater to the surface. Floodwaters and coastal waters that immerse low-lying land near waterways can also cause a natural wetland to form. Surprisingly, permafrost also causes wetlands. In Alaska, more than 174 million acres are labeled as wetlands, all formed by permafrost. Permafrost is subsoil that remains permanently frozen. This means the state hosts about 63 percent of the remaining wetlands in the United States [source: Stanford]. Although every coastal state has wetlands, they aren't just found near coasts or large rivers; water runoff from mountains can form wetlands in high mountain valleys. Every state has at least one inland wetland [source: USGS].
Some people may confuse watersheds with wetlands. The primary difference between a wetland and a watershed is that water runs off a watershed into various waterways, such as streams or creeks. The water eventually makes its way to larger bodies of water, such as oceans. A wetland collects the water between the watershed and the body of water. It acts as a filter to remove pollutants before the water collects in rivers and streams. A wetland always maintains a certain amount of water. However, a watershed becomes dry after the water runs off.
Wetlands usually are located at the bottom of valleys or in lowland areas. In a wetland, the water table is at or very near the surface: Picture a bog, marsh or swamp. They are important to the ecosystems of their regions. Wildlife and plant systems often depend on wetlands, but urban or agricultural development, along with deforestation, can threaten these important ecosystems. In British Columbia, for example, the southeast corner of Vancouver Island, the Gulf Island and nearby areas of the mainland have many swamps and marshes but most of them have been altered by human activities and some have completely disappeared [source: BC Ministry of Forests].
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