page_title: St. Johns River
section_title: Middle basin
hierarchical_section_title: St. Johns River / Geography and ecology / Middle basin
context_page_description: The St. Johns River is the longest river in the U.S. state of Florida and its most significant one for commercial and recreational use. At 310 miles long, it flows north and winds through or borders twelve counties. The drop in elevation from headwaters to mouth is less than 30 feet; like most Florida waterways, the St. Johns has a very low flow rate 0.3 mph 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 3 miles across. The narrowest point is in the headwaters, an unnavigable marsh in Indian River County. The St. Johns drainage basin of 8,840 square miles 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.
context_section_description: For 37 miles (60 km) the river passes through a 1,200-square-mile (3,100 km²) 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 of the middle basin 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 9-square-mile (23 km²) 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, passing the city of Sanford. It is at this point that the St. Johns' navigable waterway, dredged and maintained by the U.S. Army Corps of Engineers with channel markers maintained by the U.S. Coast Guard, begins. Lake Monroe, a large lake at 15 square miles (39 km²) with an average depth of 8 feet (2.4 m), drains a surrounding watershed of 2,420 square miles (6,300 km²). Sanford has adapted to the lake by building some of its downtown area on the waterfront; citizens use boat transportation and Sanford's public dock to commute into town.
  Optimally an 8-foot (2.4 m) deep channel about 100 yards (91 m) wide after leaving Lake Monroe, the St. Johns meets its most significant tributary in the middle basin, the spring-fed Wekiva River, discharging approximately 42,000,000 US gallons (160,000,000 L) a day into the St. Johns. Near this confluence are the towns of DeBary and Deltona. Forests surrounding the Wekiva River are home to the largest black bear (Ursus americanus floridanus) population in Florida; several troops of Rhesus monkeys (Macaca mulatta) 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.
  Of most vital importance to marshes are invertebrate animals, the foundation of food webs. Amphibious invertebrates such as apple snails (Pomacea paludosa), 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 (Alligator mississippiensis) 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. The marshes around the St. Johns River 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 (Eudocimus albus), wood stork (Mycteria americana), and purple gallinule (Porphyrio martinicus) 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.
caption: St. Johns River near Blue Spring State Park showing more distinct banks and trees instead of marshes
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