History

The lakes of the Upper Ocklawaha River Basin (UORB) flow in a northerly direction to form the Ocklawaha River, which continues to flow north into the St. Johns River. Lake Apopka is the largest lake in the system, comprising approximately 30,000 acres and lying at the southernmost location, thereby constituting the headwaters of the system.

In 1956, the Apopka Lock and Dam was completed. This structure was constructed to control northerly flow from Lake Apopka to Lake Beauclair through the Apopka-Beauclair Canal, which was first excavated in the 1890s. The canal was reported to lower average water levels on the lake by three to four feet. The existing system, which includes both the canal and the dam, controls the water level of Lake Apopka such that it fluctuates within a narrower range than under the previous natural condition.

At about the same time as the Apopka Lock and Dam, the Burrell Lock and Dam was constructed along Haynes Creek between Lake Eustis and Lake Griffin to control water levels within Lake Eustis, Lake Dora and Lake Harris. Over the years, the Dora Canal and Haynes Creek had been channelized so as to improve navigation between Lake Dora and Lake Eustis and between Lake Eustis and Lake Griffin. With construction of the lock and dam, water could be held within Lake Eustis, Lake Dora, Lake Beauclair and Lake Harris, stabilizing water levels when compared with the natural condition.

At the northernmost part of the system, encompassing Lake Griffin, man-made alterations started in the late 1800s with a Congressional authorization to provide for clearing the channel of obstructions to Lake Griffin, maintaining dikes to obtain a channel navigation depth of four feet to Leesburg, and constructing a lock and dam at Moss Bluff. This resulted in construction of the C-231 Canal and L-212 levee and the Moss Bluff Lock and Dam by 1924. In 1969 the C-231 Canal and L-212 were enlarged and a new Moss Bluff Lock and Dam was completed. The effect of this construction was also to stabilize water levels and reduce the frequency and severity of naturally occurring high and low water level conditions in Lake Griffin.

Since 1963, the water management districts — first the Southwest Florida Water Management District (SWFWMD) and, then in 1977, the St. Johns River Water Management District — have been authorized through legislation and agreements with local water authorities to operate and maintain the water control structures in the Ocklawaha River Basin within Orange and Lake counties. In December 1964, SWFWMD adopted regulation levels for lakes Apopka, Dora, Harris, Eustis and Griffin.

Improving water quality and managing lake levels

Through the Surface Water Improvement and Management (SWIM) program, the District has worked to improve water quality and habitat in and around the UORB lakes. Since 1988, the District has purchased more than 35,000 acres of muck farms (the drained and farmed former floodplain marshes) in the UORB. Approximately 20,000 acres were purchased by the District along the north shore of Lake Apopka, taking them out of agricultural production.

In addition to removing the former muck farms from agricultural production, the District has implemented a variety of other projects to restore floodplain wetlands and improve water quality throughout this system. The Lake Apopka Flow-Way project currently removes nutrients and suspended sediments from Lake Apopka by pumping water through large filter marshes constructed by the District. Since inception, it has removed more than 11 metric tons of total phosphorus, 375 metric tons of total nitrogen, and 18,000 metric tons of suspended solids. Rough fish harvesting on Lake Apopka and Lake Griffin has removed millions of pounds of shad, greatly reducing internal nutrient recycling because these fish feed in the sediments and excrete waste into the water column. It has also reduced turbidity caused by shad feeding activity in the lakes. The District has also restored wetland areas on Lake Griffin, which have been reconnected to the lake, thereby improving habitat for fish and wildlife.

A major aspect of the District’s program to improve water quality and other ecological conditions within the UORB Lakes involves improving water quality within Lake Apopka, which is the lake most severely impacted by nutrient enrichment and which lies at the headwaters of the system. Utilization of the approximately 20,000-acre north shore area for wetland creation and storage of surface water are major elements of this program.

To further enhance restoration efforts, District scientists have recommended changing the lake level regulation schedules so that the UORB lakes follow more closely the natural seasonal water level fluctuations based upon long-term rainfall patterns. In analyzing potentially changing these regulation schedules, District staff have completed many evaluations and held several public workshops to allow public input and understand public concerns. The two main public concerns identified in this effort were potential loss of boating access during lower water periods and potential flooding during higher water periods. Three projects were designed to address these concerns:

With completion of the Harris Bayou project, the Lake Griffin Canal Dredging Project, and the projected completion of the Lake Apopka North Shore Restoration Project, the District recently commenced final planning to improve management of water levels in the UORB lakes. The objective of this process is to implement new lake level regulation criteria for water bodies in the basin that, within flood protection constraints and navigation considerations, approximate the natural water levels and flows that occurred prior to the imposition of historic lake level regulation, for the purposes of enhancing restoration of fish and wildlife habitats and water quality, and to provide the basis for development of environmentally sound minimum flows and levels (MFLs) for the UORB lakes.

Current regulation schedule

The current regulation schedules for the UORB lakes follow the same general pattern. After March 1 of every year they require that the level of the lakes be lowered over a period of three months, until June 1, in order to increase the storage capacity of the lakes in anticipation of the seasonal rainfall that generally begins in June. The lower end of the schedule is maintained until Aug. 1, after which the lakes are permitted to steadily rise as a result of the summer rainfall to the higher end of the schedule by Nov. 1. The maximum level is then held constant throughout the remainder of the year to the following March 1, when the cycle begins again. If at any point in time during the year the water level rises above the level set by the regulation schedule, flood control-based, or essentially, maximum discharges from the system are required to return the water level to the schedule. When the water level is below the regulation schedule, an effort is made to retain water within the system by making only minimum discharges. While the range between the upper and lower ends of the regulation schedule is very narrow, the actual range of fluctuation of water levels varies substantially because of routine seasonal drought and flood conditions. However, the regulation schedule significantly lowers maximum water levels and raises minimum water elevations.

The regulation schedules include “minimum desirable” and “maximum desirable” levels. These levels were established in 1951 and were expressions of a range of water levels that were favored at a time when there was much less understanding of the role lake level fluctuation played in the environmental health of a lake. The minimum desirable level was based primarily on recreational and navigational uses. The maximum desirable level was primarily concerned with flooding. These levels have no current utility from the standpoint of managing the operation of the subject water control structures.

The current regulation schedules for the UORB lakes have a very narrow operational range; they are not desirable from the standpoint of protecting the water resources. These regulation schedules were developed in the 1950s and 1960s primarily for flood control and navigation (mainly recreational boating), with little understanding of the effects of regulation of water levels and flows on the health of UORB lakes. Based upon current scientific knowledge, it is clear that environmental issues, such as protection of fish and wildlife habitat and water quality, did not play a significant role in their development. These environmental values, as well as impacts such as flooding and navigation, must be considered in establishing minimum flows and levels.

Fluctuating lake levels

The current regulation schedules have altered the natural seasonality and the long-term range of fluctuations in water levels in the basin to the detriment of fish and wildlife habitat and water quality. They reflect an attempt to complete fluctuations within a single year and maintain similar water levels from year-to-year. They have tended to stabilize water levels compared to natural conditions by lowering maximum water elevations and raising minimum water elevations.

Lowering maximum water elevations prevents periodic increases in water levels to inundate the floodplain, which has many environmental benefits. Floodplains are a significant source of particulate organic materials, which are an important base for aquatic food chains. They provide feeding and spawning habitat and habitat for juveniles for many species of fish. Periodic flooding provides for maintenance of wetland habitats. Floods disperse seeds of wetland species, and periodic flooding is necessary for growth of wetland plants and exclusion of upland plants from wetland habitats.

Raising minimum water levels also has a number of detrimental effects. Many wetland and aquatic plants require air exposure of sediments for germination. Air-exposure also allows consolidation of lake sediments, which provides an improved substrate in which plants can root. Constant higher-water levels limit growth of aquatic plants to shallow areas where there is sufficient light for growth. Plant growth during low-water periods can allow expansion of the vegetated zone to deeper areas of the lake. Increases in minimum water levels have contributed to a decline in deep marsh and submersed aquatic vegetation in the UORB lakes.

Stabilization of water levels also has detrimental effects on lake fisheries. Aquatic vegetation in lakes and in the floodplain provides spawning sites, as well as food and habitat for juveniles of many species of fish. Additionally, consolidated lake sediments provide necessary substrate for spawning of many fish species.

Stabilization of water levels also can lead to degradation in water quality in the lakes through a number of mechanisms. Stabilization contributes to the loss of aquatic vegetation, which filters nutrients and sediments from stormwater runoff and stabilizes the lake bottom, reducing wind resuspension of bottom sediments. Wind resuspension of these sediments can increase turbidity and oxygen demand in the water column, potentially leading to algal die-offs and fish kills.

In sum, under the current regulation schedules a more-uniform seasonality of water levels has been imposed. Maximum water levels have been reduced, primarily for flood control purposes. Minimum water levels have been raised, primarily to facilitate navigation for recreational boating. There has been a reduction in long-term fluctuation ranges. These changes have contributed to deterioration in aquatic habitat, fisheries, and water quality in the UORBlakes.

Minimum flows and levels

The objective of minimum levels is to establish “the limit at which further withdrawals would be significantly harmful to the water resources or ecology of the area.” Florida Statutes provide that, “When appropriate, minimum flows and levels may be calculated to reflect seasonal variations.” The District has developed a minimum level program for lakes that seeks to achieve seasonal variation in water levels in order to avoid the significant harm to the water resources that results from maintaining constant water levels in lakes.

Under the District’s program, MFLs for lakes include three elevations. The “Minimum Frequent High” is defined to mean “a chronically high surface water level or flow with an associated frequency and duration that allows for inundation of the floodplain at a depth and duration sufficient to maintain wetland functions.” The “Minimum Average Level” is defined as “the surface water level or flow necessary over a long period to maintain the integrity of hydric soils and wetland plant communities.” The “Minimum Frequent Low” is defined as “a chronically low surface water level or flow that generally occurs only during periods of reduced rainfall. This level is intended to prevent deleterious effects to the composition and structure of floodplain soils, the species composition and structure of floodplain and instream biotic communities, and the linkage of aquatic and floodplain food webs.”

Minimum levels are based on achieving water resource related environmental objectives, as opposed to maintaining stabilized lake levels for boat access by riparian property owners. In addition to achieving environmental objectives, in seeking to prevent “significant harm” to the water resources, MFLs must take into account avoiding adverse hydrological impacts, such as the flooding of private property.

The District has engaged in a comprehensive program to establish minimum flows and levels. As of March 2008, the District had established MFLs for 124 springs and water bodies within its jurisdiction. In 2001 the District placed Lake Apopka and the Harris Chain of Lakes on the MFL priority list. The District’s initial water supply planning efforts had indicated these water bodies were a potential source of regional water supply. In accordance with District practice, these water bodies were placed on the priority list to evaluate potential regional water supply sources in the context of preventing significant harm to the water resources. Subsequent analysis indicated that these water bodies would not be a significant source of regional water supply. In addition, due to ongoing efforts to develop regulation schedules for Lake Apopka and the Harris Chain of Lakes that would achieve greater fluctuation of water levels, it was determined that MFLs needed to be developed in conjunction with development of the revised regulation schedules. As a result, it was determined that they be removed from the 2002 priority list in favor of higher priorities.