Surface-water features in Osceola County and adjacent areas, Florida

The western two-thirds of Osceola County, Fla., drains southward by way of the Kissimmee River and its tributaries; the eastern one-third drains eastward to the St. Johns River or to marshy areas that make up part of the headwaters of the St. Johns River. About 15 percent of the county is covered by several hundred lakes whose surface areas range in size from a few to several thousand acres. Much of the natural drainage has been altered by canalization or regulated by control structures. Under natural conditions streamflow is seasonal, usually high in September or October and low in May or June, in phase with the rainy season. Control structures are used to maintain lake levels within a relatively small range in stage, producing greater seasonal variations in river flow than before regulation. Dissolved-solids concentration of much of the surface water is less than 240 mg/l, in some, much less. The water typically is of calcium bicarbonate type. Color is fairly high, in water draining from swamps, where the pickup of humic acids is significant. (Kosco-USGS)