Sue Ann White, age 12, of Miami, Fla., for her question:
WHAT CAUSES FLORIDA'S EVERGLADES?
The Everglades is a vast freshwater marsh that covers much of southern Florida. Formed by centuries of constant overflow of the surplus waters of Lake Okeechobee after heavy rains, the Everglades extends south from the lake for about 110 miles and has a total area of almost 5,000 square miles.
The marsh lies in a great basin of limestone, the outcrop of which appears a few.miles north of Cape Sable at the southernmost tip of Florida and extends north to Lake Okeechobee. Tidal bays, lakes and connecting waterways, varying in depth from one foot to seven feet and sometimes less during the periods of least rainfall, honeycomb the wilderness of swamp, savanna and virgin forest that makes up the Everglades.
Several small streams, such as the Miami, Little and New rivers on the east and the Shark and Harney on the southwest, drain the region, but none flows into it.
Most of the great morass, however, is covered with a growth of saw grass that rises from three to 10 feet above the surface of the water and is so dense that passage through the region is effectively barred except in boats following the windings of the natural water lanes.
Cypress, mangrove thickets, palms, live oaks, bays and lush vegetation cover the numerous islets (known as hammocks) that are found in the Everglades. The highest land of the Everglades is only about seven feet above sea level and in the summer rainy season large areas of land become swamp or are covered by water.
The Everglades comprises one of the wildest and most inaccessible areas in the United States. Wildlife is abundant and largely protected within the Everglades National Park.
Inhabitants of the Everglades are almost entirely limited to several hundred Seminole.
In the late 19th and early 20th centuries large drainage programs were undertaken. Canals were dug to lower the level of Lake Okeechobee and prevent the overflowing of its waters.
On a section of drained land in the area south of the lake, farmers today grow fruit, vegetables and sugar cane.
The Cross Florida Waterway, opened in 1937, passes through the Everglades and connects the Atlantic ocean with the Gulf of Mexico. Two major highways cross the Everglades.
In 1947 the Everglades National Park was established. This park contains the largest sub tropical wilderness in the United States.
Located in the heart of the Everglades, the park extends about 45 miles north along the Gulf of Mexico from Cape Sable. The region has both freshwater and saltwater areas and is noted for its distinctive plant and animal life.
The establishment of the park was first authorized by Congress in 1934, but economic difficulties and opposition to its development caused a 13 year delay. In 1970 construction of an international airport near the park was halted after much debate on the airport's impact on the environment.