Saint Johns River, navigable stream of northeastern Florida, U.S., the longest river in the state. It rises in swamps in Brevard county southwest of Melbourne, in the east-central part of the state and flows north parallel to the Atlantic coast until it turns at Jacksonville to empty into the ocean, 15 miles (25 km) to the east, after a course of 300 miles (485 km). The river forms several large lakes, including Lake George on the eastern side of Ocala National Forest. Its principal tributary is the Oklawaha River, which flows north along the western side of the forest before turning eastward. The St. Johns is navigable from Sanford to its mouth, a distance of some 200 miles (320 km). It becomes a broad estuary north of Palatka and east of Jacksonville, where it has its deepest channel at about 40 feet (12 metres) and is a marsh. Over its entire course it has a fall of less than 30 feet (9 metres), and tidal currents reach far upstream.
The St. Johns River drains an area with many swamps and lakes, a region of pine groves as well as farm- and pastureland. The river is important both for shipping and for recreation, especially fishing. It went through several names before finally being called San Juan by the Spanish in the late 16th century; the British translated it to St. Johns in the late 18th century. Recreation areas along its course, in addition to the national forest, include Blue Spring State Park, Lake Woodruff National Wildlife Refuge, and Silver Glen Springs Recreation Area.