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.