St. Johns River
The St. Johns River is the longest river in the U.S. state of Florida and is the most significant one for commercial and recreational use. At long, it flows north and winds through or borders 12 counties. The drop in elevation from headwaters to mouth is less than ; like most Florida waterways, the St. Johns has a very slow flow speed of, and is often described as "lazy".
Numerous lakes are formed by the river or flow into it, but as a river its widest point is nearly across. The narrowest point is in the headwaters, an unnavigable marsh in Indian River County. The St. Johns drainage basin of includes some of Florida's major wetlands. It is separated into three major basins and two associated watersheds for Lake George and the Ocklawaha River, all managed by the St. Johns River Water Management District.
Although Florida was the location of the first permanent European settlement in what would become the United States, much of Florida remained an undeveloped frontier into the 20th century. With the growth of population, the St. Johns, like many Florida rivers, was altered to make way for agricultural and residential centers, suffering severe pollution and redirection that has diminished its ecosystem. The St. Johns, named one of 14 American Heritage Rivers in 1998, was number 6 on a list of America's Ten Most Endangered Rivers in 2008. Restoration efforts are underway for the basins around the St. Johns as Florida's population continues to increase.
Historically, a variety of people have lived on or near the St. Johns, including Paleo-indians, Archaic people, Timucua, Mocama, Mayaca, Ais, French, Spanish, and British colonists, Seminoles, slaves and freemen, Florida crackers, land developers, tourists and retirees. It has been the subject of William Bartram's journals, Harriet Beecher Stowe's letters home, and Marjorie Kinnan Rawlings' books. In the year 2000, 3.5 million people lived within the various watersheds that feed into the St. Johns River.
Geography
Starting in Brevard County and meeting the Atlantic Ocean at Duval County, the St. Johns is Florida's primary commercial and recreational waterway. It flows north from its headwaters, originating in the direction of the Lake Wales Ridge, which is only slightly elevated at above sea level. Because of this low elevation drop, the river has a long backwater. It ebbs and flows with tides that pass through the barrier islands and up the channel. Uniquely, it shares the same regional terrain as the parallel Kissimmee River, although the Kissimmee flows south.Upper basin
The river is separated into three basins and two associated watersheds managed by the St. Johns River Water Management District. Because the river flows in a northerly direction, the upper basin is located in the headwaters at its southernmost point. The river begins as a network of marshes in Indian River County, at a point west of Vero Beach aptly named the St. Johns Marsh. It is a blackwater stream, meaning that it is fed primarily by swamps and marshes lying beneath it; water seeps through the sandy soil and collects in a slight valley. The upper basin measures approximately ; the St. Johns transforms into a navigable waterway in Brevard County. The river touches on the borders of Osceola and Orange Counties and flows through the southeast tip of Seminole County, transitioning into its middle basin a dozen miles or so north of Titusville.The upper basin was significantly lowered in the 1920s with the establishment of the Melbourne Tillman drainage project. This drained the headwaters eastward to the Indian River through canals dug across the Ten-Mile Ridge near Palm Bay. In 2016 the U.S. Army Corps of Engineers completed a restoration project, returning natural flow to much of the area.
The river is at its narrowest and most unpredictable in this basin. Channel flows are not apparent and are usually unmarked. The most efficient way to travel on this part of the river is by airboat. Approximately 3,500 lakes lie within the watershed; all are shallow, with maximum depths between. The river flows into many of the lakes which further confuses navigation. Eight larger lakes and five smaller ones lie in the upper basin; one of the first is named Lake Hell 'n Blazes, referencing oaths yelled by boatmen and fishermen in the early 19th century, frustrated when trying to navigate through floating islands of macrophytes, or muck and weeds, as the islands changed location with the creeping flow. Lakes Washington, Winder, and Poinsett are located further along this stretch of the river. The northernmost points of the upper basin contain the Tosohatchee Wildlife Management Area, created in 1977 to assist with filtration of waters flowing downstream.
Wetlands in the upper and middle basin are fed by rainwater trapped by the structure of the surrounding land. It is an oxygen- and nutrient-poor environment; what grows usually does so in peat which is created by centuries of decaying plant material. Water levels fluctuate with the subtropical wet and dry seasons. Rain in central and north Florida occurs seasonally during summer and winter, but farther south rain in winter is rare. All plants in these basins must tolerate water fluctuation, both flooding and drought. Sweetbay, cypress, and swamp tupelo trees often find great success in this region on raised land called hammocks. Trees that live in water for long periods usually have buttressed trunks, tangled, braided roots, or protrusions like cypress knees to obtain oxygen when under water, but the majority of plant life is aquatic. Wetland staples include the American white waterlily, pitcher plants, and Virginia iris. In the southernmost points of the river, Cladium, or sawgrass, grows in vast swaths of wet prairie that at one time extended into the Everglades. These wetland flora are remarkably successful in filtering pollutants that otherwise find their way into the river.
Middle basin
For the river passes through a basin fed primarily by springs and stormwater runoff. This basin, spreading throughout Orange, Lake, Volusia, and Seminole Counties, is home to the greater Orlando metropolitan area, where two million people live and major tourist attractions are located. The topography varies between clearly distinguishable banks along the river and broad, shallow lakes. Two of the largest lakes in the middle basin are created by the river: Lake Harney and Lake Monroe. The shallow Lake Harney is fed by the long narrow Puzzle Lake; immediately north is the Econlockhatchee River, which joins to increase the volume of the St. Johns to where navigation becomes easier for larger boats. The river veers west, touching on Lake Jesup before it empties into Lake Monroe near Sanford. It is at this point that the St. Johns' navigable waterway begins, which is dredged and maintained by the U.S. Army Corps of Engineers with channel markers maintained by the U.S. Coast Guard. Lake Monroe, a large lake at with an average depth of, drains a surrounding watershed of.Optimally an deep channel about wide after leaving Lake Monroe, the St. Johns meets its most significant tributary in the middle basin, the spring-fed Wekiva River, discharging approximately per day into the St. Johns. Forests surrounding the Wekiva River are home to the largest black bear population in Florida; several troops of Rhesus monkeys have adapted to live near the river as well. The monkeys' introduction to Florida is unclear; they were reportedly brought either to serve in backdrop scenes of Tarzan movies filmed around the Silver River in the 1930s, or to lend an air of authenticity to "jungle cruises" provided by an enterprising boat operator around the same time.
Springs in Florida stay at an even temperature of throughout the year; because of this, Blue Spring is the winter home for West Indian manatees, and they are protected within Blue Spring State Park. Manatees are large, slow-moving herbivorous aquatic mammals whose primary threats are human development and collisions with swiftly moving watercraft. Many parts of the St. Johns and its tributaries are no-wake zones to protect manatees from being critically or fatally injured by boat propellers. Human interaction with manatees in Blue Spring State Park is forbidden.
Of most vital importance to marshes are invertebrate animals, the foundation of food webs. Amphibious invertebrates such as apple snails, crayfish, and grass shrimp consume plant material, hastening its decomposition and acting as a food source for fish and birds. Insect larvae use water for breeding, feeding upon smaller copepods and amphipods that live in microscopic algae and periphyton formations. Mosquitos, born in water, are in turn the favorite food of 112 species of dragonflies and 44 species of damselflies in Florida. These animals are water hardy and adaptable to dry conditions when water levels fluctuate from one season to the next or through drought and flood cycles.
Of vertebrates, numerous species of frog, salamander, snake, turtle, and alligator proliferate in marsh waters. Most of these animals are active at night. Frog choruses are overwhelming; during alligator mating season the grunts of bulls join in. River otters can be found through the length of the St. Johns and its tributaries, living in burrows or in the roots of trees bordering waterways. They eat crayfish, turtles, and small fish, and are active usually at night, playful but shy of human contact. The marshes around the upper basin teem with birds. A recent study counted 60,000 birds in one month, nesting or feeding in the upper basin. Wading and water birds like the white ibis, wood stork, and purple gallinule depend on the water for raising their young: they prey upon small fish and tadpoles in shallow water and puddles in the dry season. In successful seasons, their colonies can number in the thousands, creating a cacophony of calls and fertilizing trees with their droppings.