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Water bodies, watersheds and storm water

The St. Johns River

Florida’s longest river is a liquid chameleon. During its slow 310-mile journey, the St. Johns River morphs from a marsh in Indian River County into a broad waterway with expansive views as it flows to northeast Florida and into the Atlantic Ocean.

A limpkin forages for food.

A limpkin forages for food.

The sawgrass marsh areas of the river’s headwaters are teeming with alligators, wading birds and waterfowl. In Brevard County, the marsh becomes a navigable river, gently twisting as it crawls north. Then the river reveals a tapestry of lakes, bottle-clear spring runs and darkwater tributaries. As the river leaves Putnam County for Clay and St. Johns counties, it widens considerably, in some locations exceeding two miles across. After passing Mayport in Duval County, the longest river contained in the state of Florida ends its journey where it mixes with the Atlantic Ocean.

Alligators can be found along the river and its tributaries.

Alligators can be found along the river and its tributaries.

The St. Johns River is an ancient intracoastal lagoon system. As sea levels dropped, barrier islands became an obstacle that prevented water from flowing east to the ocean. The water collected in the flat valley and slowly meandered northward, forming the St. Johns River. Wildlife is abundant in and around the St. Johns River. For hundreds of years, the river has been home to many plant species and marine animals — manatees, largemouth bass and many other types of fish, crabs, shrimp and other shellfish, river otters, waterfowl, blue herons and bald eagles, and alligators and other reptiles.

The north-flowing St. Johns — one of the few rivers in the United States that flows north — is one of the laziest rivers in the world. From its source in the marshes south of Melbourne to its mouth in Mayport, the river drops a total of less than 30 feet — or about one inch per mile. The incoming tide from the Atlantic Ocean causes the river to reverse its flow twice a day and in periods of low water, tides may cause a reverse flow as far south as Lake Monroe — 161 miles upstream from the river’s mouth. High and sustained northeasterly winds can result in many days of reversed flow. Because the river flows slowly and reverses course regularly, it is difficult for the river current to naturally flush pollutants.

The river gets its tea color from tannins, a natural color caused by decaying plant material.

Aquatic grasses provide habitat and food for wildlife.

Aquatic grasses provide habitat and food for wildlife.

The land area that drains into a water body is called a drainage basin or “watershed.” The St. Johns River is divided into three drainage basins. Because the river flows north, the upper basin is the area to the south that forms its marshy headwaters in Indian River and Brevard counties. The middle basin is the area in central Florida where the river widens, forming lakes Harney, Jesup, Monroe and George. The lower basin is the area in northeast Florida from Putnam County to the river’s mouth in Duval County, where the river empties into the Atlantic Ocean.

Major tributaries, or smaller streams and rivers that flow into the St. Johns River, include the Wekiva River, the Econlockhatchee River and the Ocklawaha River.

Despite its mystery and beauty, the river faces challenges. For decades, human activities have degraded water quality in portions of the river. The main culprits are stormwater runoff from urban areas, treated domestic and industrial wastewater and agricultural runoff from farming areas. These pollutants can trigger algal blooms (caused by nutrient-rich discharges) and subsequent fish kills.

The tannin-stained waters of the St. Johns are woven into the life of northeast Florida. It is rich in history and culture, holds environmental and aesthetic value, plays an important role in the economy and serves as a place to call home for people and wildlife alike.


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St. Johns River Water Management District
4049 Reid Street, Palatka, FL 32177
(800) 725-5922