Because of the importance of lakes to residents of central Florida and the many questions and misconceptions about lakes, this primer was prepared by the U.S. Geological Survey (USGS) in cooperation with the St. Johns River Water Management District and the South Florida Water Management District. The USGS has been collecting hydrologic data in central Florida since the 1920s, obtaining valuable information that has been used to better understand the hydrology of the water resources of central Florida, including lakes. In addition to data collection, as of 1994, the USGS had published 66 reports and maps on central Florida lakes (Garcia and Hoy, 1995).
The main purpose of this primer is to describe the hydrology of lakes in central Florida, the interactions between lakes and ground- and surface-waters, and to describe how these interactions affect lake water levels. Included are descriptions of the basic geology and geomorphology of central Florida, origins of central Florida lakes, factors that affect lake water levels, lake water quality, and common methods of improving water quality. The geographic area discussed in this primer is approximate (fig. 1) and includes west and east-central Florida, extending from the Gulf of Mexico to the Atlantic Ocean coastlines, northward into Marion, Putnam, and Flagler Counties, and southward to Lake Okeechobee. The information presented here was obtained from the many publications available on lakes in central Florida, as well as from publications on Florida geology, hydrology, and primers on ground water, surface water, and water quality. Many publications are available that provide more detailed information on lake water quality, and this primer is not intended as an extensive treatise on that subject. The reader is referred to the reference section of this primer for sources of more detailed information on lake water quality. Lakes discussed in this report are identified in figure 2. Technical terms used in the report are shown in bold italics and are defined in the glossary.
The classification of some water bodies as lakes is highly subjective. What one individual considers a lake another might consider a pond. Generally, any water- filled depression or group of depressions in the land surface could be considered a lake. Lakes differ from swamps or wetlands in the type and amount of vegetation, water depth, and some water-quality characteristics. Lakes typically have emergent vegetation along the shoreline with a large expanse of open water in the center. Swamps or wetlands, on the other hand, are characterized by a water surface interrupted by the emergence of many varieties of plant life, from saw grasses to cypress trees.
Lakes may be naturally formed or manmade; however, the distinction between naturally formed and manmade lakes is not always clear. For example, retention ponds, which are required for the treatment of stormwater, can be constructed so that they serve multiple purposes of stormwater treatment and aesthetic enhancement of property. Larger retention ponds sometimes are used by residents for boating and fishing and are considered by some to be lakes.
In addition to aesthetic value and recreational uses, lakes in central Florida are extremely important as habitats for fish, alligators, turtles, and birds such as hawks, eagles, ducks, and herons. Because Florida lakes are used and enjoyed by many, they need to be appreciated, understood, and managed for the benefit of all.
Hydrologic characteristics of central Florida lakes vary widely. The surface areas of lakes can range from several hundred square miles, such as Lake Okeechobee, to less than an acre. Water levels in some lakes may vary by 10 feet or more, whereas in other lakes, the water level may vary by only 1 or 2 feet. The quality of water among lakes in central Florida also is variable, from pristine lakes such as Lake Butler in west Orange County to the pea-green-colored waters of Lake Apopka, a short distance to the north in Orange and Lake Counties (although the clarity of water is not necessarily an indication of the quality of the water). Some lakes have natural surface-water inlets and outlets. Other lakes are landlocked, receiving water only from rainfall and losing water only from evaporation and seepage into the surrounding soils. This great variety in hydrologic characteristics is one of the reasons why water levels vary among lakes and why lakes respond differently to rainfall.