They occur in every state, from the coastal marshes of Alaska to the mangrove forests of Florida. Some are dry on the surface most of the year and others remain saturated or even inundated. There are two main categories of wetlands - coastal and inland. Coastal wetlands occur near the ocean and are closely linked with estuaries, where sea water mixes with fresh water. Inland wetlands occur everywhere from plains to mountain tops.
Some wetlands exist along the coast, like estuaries, but they can also exist inland.
Bogs are found in colder regions of the world where the temperatures and limited oxygen in the water discourage the breakdown of organic material. Unlike bogs, fens are not acidic and can support a more diverse plant and animal community. Like bogs, fens are found in northern regions. Freshwater marshes - 90 percent of our nation's wetlands. They are open areas, usually with few trees and shrubs.