What is a Watershed?
Water bodies are often referred to alternately as "watersheds". A watershed is a ridge of high(er) land dividing two areas that are drained by different river systems. A watershed is the region draining into a river, river system, or other body of water. To learn more about watersheds please visit EPA's Watershed Academy.
How Do Watersheds Work?
How a watershed is shaped will determine how it drains, where flooding occurs, and how water quality is affected. In addition to the shape or morphology of the physical system there are also weather processes that affect water quantity and quality. The following graphic shows how water moves through watersheds. This process is called the hyrologic cycle.
Lee County's Watershed History
The natural surface water hydrology of Southwest Florida has resulted from the interaction of the region's subtropical climate with its topography and geology. Lee County's watershed was once part of the huge Everglades ecosystem in which slowly moving sheet flows of water drained to the Gulf of Mexico. Under natural conditions, water flow in the basin generally moved south to southwestward from the Immokalee Rise, providing fresh water to the estuaries along the southwest coast. Lee County currently drains into two major basins; the Caloosahatchee River Basin and the Estero Bay Basin. As canals and levees were built to control flooding and drain large areas for agricultural and residential use, hydrologic connections among different parts of the Everglades ecosystem were severed.
Human Impacts Over Time
Today, the natural freshwater sheet-flow patterns have been significantly altered, resulting in drought conditions and major fire hazards during the dry season and excessive stormwater runoff during the wet season. Consequently, salinity patterns have changed, nutrient loadings have increased, and the numbers of seagrasses, fisheries, and shellfish have been reduced.
Lee County's Watersheds Now
Charlotte Harbor is America's 17th largest estuary and Florida's 2nd largest open-water estuary. It is semi-enclosed by Cape Haze and the barrier islands of Gasparilla, Boca Grande, Cayo Costa, Captiva and Sanibel on the western side of the habor and inland masses that make up Sarasota, Charlotte and Lee County on the eastern side of the harbor. The harbor opens to the Gulf of Mexico through several tidal inlets between the barrier islands. Its open-water surface area is about 270 square miles (Charlotte Harbor National Estuary Program [CHNEP], 1998) and averages 7 feet in depth (Stoker, 1992).
The drainage basin stretches from the headwaters of the Peace River in Polk County, southward through San Carlos Bay near Fort Myers, and eastward to Lake Okeechobee, encompassing 8 counties and 4,670 square miles (Stoker, 1992). Charlotte Harbor receives its fresh water from three major rivers and several smaller streams that mix with the marine waters of the Gulf of Mexico. The salinity can range from freshwater to seawater depending on the season, location and depth in the harbor.
The Charlotte Harbor region is home to five national wildlife refuges, five state aquatic preserves, and one state buffer preserve. The region supports a great diversity of semitropical plant and animal life. In 1990, 86 federal and state protected plant and animal species were found. In 1995, Charlotte Harbor was recognized as an "estuary of national significance" and was accepted into the National Estuary Program. The CHNEP study area, at 4,400 square miles, differs slightly from the 4,670 square-mile drainage basin depicted by the U.S. Geological Survey (USGS) (Stoker, 1992). The study area adds the Estero, Lemon, Dona, and Roberts Bay watersheds but does not include the non-tidal portions of the Caloosahatchee River watershed between Franklin Lock and Lake Okeechobee.
The Caloosahatchee River Basin which rises less than 15 feet in elevation through Lee, Hendry, and Glades Counties follows the river from Lake Okeechobee to San Carlos Bay. Historically, the Caloosahatchee River originated as overland flow from Lake Okeechobee through marshlands and swamp forest (CHNEP, 2000a). The modern Caloosahatchee River (C-43) is a channelized flood control and navigational waterway, maintained by the U.S. Army Corps of Engineers (USACOE) as part of the Okeechobee Waterway, which links the Gulf of Mexico to the Atlantic Ocean via Lake Okeechobee and the Lucie Canal and River. Three lock and spillway structures control the river from Lake Okeechobee to San Carlos Bay. The Moore Haven Lock and Spillway (S-77), on the western shore of Lake Okeechobee, regulates lake waters and lowers the water from Lake Okeechobee down to 11 feet NGVD (National Geodetic Vertical Datum). The Ortona Lock and Spillway (S-78) helps to control water levels on adjacent lands upstream, lowers the water downstream to 3 feet NGVD, and separates the C-43 into eastern and western basins. The Franklin Lock and Dam, near Olga in Lee County, artificially separates the fresh water of the Caloosahatchee River from the salt water of the estuary. It lowers the water level to 1 foot NGVD, regulates freshwater discharge into the estuary, and acts as an impediment to saltwater intrusion upriver. It also marks the beginning of the 30-mile tidal basin of the Caloosahatchee River, which starts at the lock and continues to the Gulf of Mexico (Capece et al., 1997; SFWMD, 2000a).
Estero Bay is a shallow, subtropical lagoon (11,317 acres) separated from the Gulf by barrier islands. Seagrass beds are common in the bay, but high turbidity restricts seagrasses to shallow depths. The Estero and Imperial Rivers and Spring, Mullock, and Hendry Creeks, although small, are the major tributaries in this area. The Estero Bay Basin was, and in many areas still is, typical of low, flat, southern Florida lands dominated by wetlands and characterized by slow, sheet-flow drainage patterns. In the past, the naturally dispersed water patterns distributed nutrients over broad areas of wetland vegetation. Seasonal fluctuations in flow from rainfall created the necessary salinity regime in Estero Bay for good estuarine productivity. Increasing development in the 1960s led to changes in the natural river systems around Estero Bay, altering freshwater inflow patterns.
This information provided courtesy of the Florida Department of Environmental Protection and the South Florida Water Management District. For more information about the physiographic and geographic history and current conditions of Lee County's watersheds the FDEP Bureau of Water Resource Management website to access FDEP's Basin Status Reports.
For more information about Lee County's Water Quality Program please contact Karen Bickford at firstname.lastname@example.org or 239-533-8706.