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ing the rainy season and is grassland at other times. The Okavango is a popular tourist destination because it is home to a rich variety of wildlife, including Africa’s largest elephant population and more than 400 species of birds. The Wadden Sea is Europe’s largest tidal wetland. Protected from the North Sea by the Friesian Islands, the Wadden Sea stretches 310 miles (500 km) along the coasts of the Netherlands, Germany and Denmark. It is a combination of islands, sandbanks, salt marshes and tidal flats, covering a total area of 3,800 square miles (10,000 sq. km). The area is a vital stopover place for migrating birds and fish. How Wetlands Change A wetland is constantly undergoing change—growing, shrink- ing, or altering shape. These changes are affected by the amount of water entering or leaving the wetland and the amount of material carried by the water. Other changes are governed by plant growth and chemical reactions. Rivers and streams are forever carving and shaping their own beds and edges, removing soil from their banks and carry- ing it downstream. In addition they also carry material washed down into them by rainfall. The bigger the river, the more sediment it carries. A flooding river can deposit millions of tons of soil over its floodplain. When it reaches the sea the river deposits all its remaining sediment. Deltas are built as these sediments are gradually spread along the coast to either side of the river’s mouth. In most wetlands, the amount of water changes with the seasons. In some places the river floodplains may show no sur-

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Wetlands