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water. An estuary is where a river widens as it joins the sea. A delta is an estuary that has silted up, so that the river fans out into many channels as it joins the sea. Between the channels and lagoons are reed-beds and expanses of tidal mud (tidal flats). The mud in an estuary is rich in nutrients because where fresh and salt water meet, chemicals and nutrient parti- cles cling together and settle on the river bed. Lakes often have wetland systems such as marshes and swamp forests around their shallows. Some lakes have con- stant inflows and outflows of water, while others have no out- lets—they lose water only by evaporation . Lakes of this second type sometimes become “salt” lakes, because minerals in the lake (“salts”) become more concentrated as the water evapo- rates. The Planet’s Major Wetland Areas The Florida Everglades consist of grass and sedge marshlands, cypress swamps, and coastal mangroves. They are regularly flooded when Lake Okeechokee in the north overflows, but the flood area has been reduced in recent years to accommodate growing human communities. The Everglades once covered over 4,000 square miles (10,360 sq. km), but it is now about half that size. Some 2,360 square miles (6,109 sq. km) are man- aged by the National Park Service as Everglades National Park, the largest protected wilderness area east of the Rocky Mountains within the United States. The South American Pantanal is one of the Earth’s largest floodplains. It covers about 75,000 square miles (200,000 sq. km) of Brazil, Bolivia, and Paraguay, and is full of lakes, marsh-

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Wetlands