In Florida, the level of a lake may be dependent upon many factors including weather patterns, surface soil types, nearby groundwater pumping, and hydrogeologic conditions, such as "perched" groundwater—water held in sands below the surface but typically separated from deeper groundwater by layers of clay, or even rock—and connection to deep aquifer sources (such as the Floridan aquifer).
Staff gage showing vertical datum. Source: SWFWMD
When the weather is dry, lake levels are often low and with abundant rain, lake levels generally rise. This is due to dependence of many Florida lakes on lateral seepage from perched groundwater systems into the lake. (“Perched” groundwater is a layer or pocket of groundwater that is segregated from the main water table by nonporous material like impermeable rock or clay.) Other lakes are highly dependent on available surface water, actual rainfall and/or stormwater runoff. A smaller number of Florida lakes are “spring fed,” meaning that their water supply is mostly from deep aquifer sources where water flows up and into the lake.
If you plan to build a lakefront home or a dock, it's a good idea to find out what the historic water levels are for a lake. Such information can be crucial to the success of your project. Failure to do so could result in unexpected flooding or the opposite; during drought conditions, some lakefront residents may be surprised to find their lake has suddenly shrunk out of sight.
Aside from weather patterns, there are a few other naturally occurring factors that can affect water levels. Geology can have a lot to do with a lake's ability to “hold” water. For instance, lakes with sandy or porous soils are more susceptible to losing water through seepage, whereas clay soils can act as a barrier and help lakes retain water. Evaporation is another major factor. For example, in central Florida, evaporation rates range from 25 inches to 50 inches per year!
Fluctuations in lake levels may also be the result of human activity such as water withdrawal for drinking and irrigation, channelization, dams, dredge and fill projects, and shoreline development.
Dock out of water due to low levels.
So how does one know whether a lake level is low, high or “normal”? Thanks to a legislative mandate (Section 373.042 of the Florida Statutes), Florida's Water Management Districts are required to estimate minimum flows and levels (MFL): minimum water levels for lakes and minimum flows for streams. Each district has a section on its website with documents describing the analysis and results and the mandated flow/level for water bodies within its purview.