Here’s how wetlands help control flooding in Central Florida

Clearly, Lake Jesup in Seminole County is a lake. But it’s also a watershed, made up of dozens of different sources of water all ultimately feeding into the lake: like rivers, ditches, canals and other lakes.

Lake Jesup is one of five major watersheds within a larger drainage basin, the Middle Basin of the St. Johns River. The St. Johns is Florida’s longest river, flowing 310 miles from its marshy starting point in Indian River County up to Jacksonville, where it empties into the Atlantic Ocean.

The St. Johns River flows south to north, which actually isn’t too unusual. Like anything else, rivers follow gravity, chasing the path of least resistance.

But since the St. Johns River is very flat, barely fluctuating in elevation from start to finish, it tends to move slowly — making it one of the world’s laziest rivers, according to the nonprofit St. Johns Riverkeeper. During times of heavy rainfall, excess water can accumulate and make the river rise, especially at bottleneck points where the St. Johns narrows.

The St. Johns also widens at different points along its long and winding journey, illustrating the origin of its Seminole-Creek name, Welaka: “river of lakes.” Lake Jesup is a good example, according to Alex Roberts, a field program supervisor with the St. Johns River Water Management District.

“Lake Jesup, it’s called a lake, but it’s part of the river, technically,” Roberts said. “Looks like a lake, acts like a lake, functions like a lake … It's just a very wide basin in the river.”