The St. Johns River (officially Saint Johns River, but commonly spelled St. John's River) is the longest river in the U.S. state of Florida, stretching 310 miles (500 km) from Indian River County to the Atlantic Ocean in Duval County. The St. Johns River is the second longest river in the United States that flows in a generally northwards direction. It was designated as one of the American Heritage Rivers in 1997.
The elevation change from headwaters to mouth is only about 30 feet, making the St. Johns one of the world's "laziest" rivers . Its extremely low velocity, combined with the generally level elevation, causes the St. Johns to spread out to a great width for much of its course. During periods of low flow, the river can be influenced by tides as far south as Lake Monroe - 161 miles inland . For a distance of over twenty miles before arriving at downtown Jacksonville, the river's average width exceeds two miles, and in some places, exceeds three miles in width. The slow flow of the St. Johns makes it difficult for pollutants to be flushed from the waters, which has become a serious problem for the river ecosystem . Still, the river is home to numerous species of plants and animals. It is not uncommon to see dolphins in the river east of Jacksonville and manatees in the springtime when the water warms up. Alligators, bald eagles, ospreys, stingrays, and many species of fish—both salt and fresh water—are found living in the river and on its banks. The entire basin is managed by the St. Johns Water Management District.
