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Natural freshwater lake in Florida, United States

Lake Okeechobee (/US//oʊ//k//i/'/tʃ//oʊ//b//i/ ohkeeCHOHbee) is the largest freshwater lake in the U. S. state of Florida. It is the tenth largest natural freshwater lake among the 50 states of the United States and the second largest natural freshwater lake contained entirely within the contiguous 48 states, after Lake Michigan. Okeechobee covers 730 square miles (1,891 km2) and is exceptionally shallow for a lake of its size, with an average depth of only 9 feet (3 m). It is not only the largest lake in Florida or the largest lake in the southeast United States, but it is too large to see across. The Kissimmee River, located directly north of Lake Okeechobee, is the lake's primary source. The lake is divided between Glades, Okeechobee, Martin, Palm Beach and Hendry counties. All five counties meet at one point near the center of the lake.

The earliest recorded people to have lived around the lake were the Calusa. They called the lake Mayaimi, meaning "big water", as reported in the 16th century, by Hernando de Escalante Fontaneda. The name Okeechobee comes from the Hitchiti words oki (water) and chubi (big). Slightly later in the 16th century, René Goulaine de Laudonnière reported hearing about a large freshwater lake in southern Florida called Serrope. By the 18th century the largely mythical lake was known to British mapmakers and chroniclers by the Spanish name Laguna de Espiritu Santo. In the early 19th century it was known as Mayacco Lake or Lake Mayaca after the Mayaca people, originally from the upper reaches of the St. Johns River, who moved near the lake in the early 18th century. The modern Port Mayaca on the east side of the lake preserves that name. On the southern rim of Lake Okeechobee, three islands—Kreamer, Ritta, and Torey—were once settled by early pioneers. These settlements had a general store, post office, school, and town elections. Farming was the main vocation. The fertile land was challenging to farm because of the muddy muck. Over the first half of the twentieth century, farmers used agricultural tools—including tractors—to farm in the muck. By the 1960s, all of these settlements were abandoned. All of Lake Okeechobee was included in the boundaries of Palm Beach County when it was created in 1909. In 1963, the lake was divided among the five counties surrounding the lake.

In 1926, the Great Miami Hurricane hit the Lake Okeechobee area, killing approximately 300 people. Two years later in 1928, the Okeechobee Hurricane crossed over the lake, killing thousands. The Red Cross reported 1,836 deaths, a figure which the National Weather Service initially accepted, but in 2003, the number was revised to "at least 2,500". In both cases the catastrophe was caused by flooding from a storm surge when strong winds drove water over the mud dike that circled the lake at the time. After the two hurricanes, the Florida State Legislature created the "Okeechobee Flood Control District". The organization was authorized to cooperate with the U. S. Army Corps of Engineers in actions to prevent similar disasters. U. S. President Herbert Hoover visited the area personally, and afterward the Corps designed a plan incorporating the construction of channels, gates, and nearly 140 miles of levees to protect areas surrounding Lake Okeechobee from overflow. However, the lake's level began dropping soon after and by July 2007, it had dropped more than 4 feet (1 m) to its all time low of 8.82 feet (3 m). In August 2008, Tropical Storm Fay increased water levels to above sea level, the first time it exceeded since January 2007. Over a seven day period (including some storms that preceded Fay), about of rain fell directly onto the lake. Through early 2008, the lake remained well below normal levels, with large portions of the lake bed exposed above the water line. During this time, portions of the lake bed, covered in organic matter, dried out and caught fire. In late August 2008, Tropical Storm Fay inundated Florida with record amounts of rain. Lake Okeechobee received almost a increase in water level, including local run off from the tributaries. In 2013, heavy rains in central Florida resulted in high runoff into the lake; rising lake levels forced the CoE (Army Corps of Engineers) to release large volumes of polluted water from the lake through the St. Lucie River estuary to the east and the Caloosahatchee River estuary to the west. Thus the normal mix of fresh and salt water in those estuaries was replaced by a flood of polluted fresh water resulting in ecological damage. Since 2013, the CoE has been forced to pump billions of gallons of water out of the lake to avoid jeopardizing the integrity of the Hoover dike holding back the water from inundating the surrounding populated area. Some claim that sugar plantations have been pumping polluted water from their flooded fields into the lake, but U. S. Sugar claims back pumping is only to avoid flooding of communities, never to protect farmland. In March 2015, the rate was daily. This results in pollution problems for the Treasure Coast, St. Lucie estuary, and the Indian River Lagoon. In May 2016, 33 square miles (85 km2) of the southern portion of the lake were affected by an algal bloom. The outbreak was possibly due in part to nutrient laden waters reaching the lake from farms and other sources. Microcystin was found among the other species involved in the outbreak. On June 23, 2017, the South Florida Water Management District was granted emergency permission to back pump clean water into Lake Okeechobee to save animals and plants in bloated water conservation areas."

The 100 feet (30 m) wide dike surrounding Lake Okeechobee is the basis for the Lake Okeechobee Scenic Trail (LOST), a part of the Florida National Scenic Trail, a 1300 mile (2092 km) trail. There is a well maintained paved pathway along the majority of the perimeter, although with significant breaks. It is used by hikers and bicyclists, and is wide enough to accommodate vehicles.

The most common fish in this lake are largemouth bass, crappie, and bluegill. Pickerel have been less commonly caught.

This shallow lake has been previously studied for its algal blooms. Lake Okeechobee is known for its algal blooms in consequence of increased eutrophication. Algal blooms like this can be harmful to the environment, including the lake's flora and fauna, because of released toxins. The vegetation at Lake Okeechobee is important in maintaining the oxygen in the lake on which many aquatic biota rely. There are various species of biota in Lake Okeechobee that are interdependent on each other for food, habitat, and other resources. Multiple limnological studies and related research has been conducted at Lake Okeechobee.

Lake Okeechobee is shallow lake, with an average depth of only , and has a fetch of In total, the lake has a surface area of The lake is normally mixed, but on days with direct sunlight and limited wind, the lake can exhibit diurnal thermal stratification. Although daily thermal stratification is brief, a hypolimnion can form during this time resulting in decreased amounts of dissolved oxygen at the lake bottom. Lake transparency, measured as secchi depth, is found to be inversely correlated with the amount of suspended solids in the lake. Suspended solids varied with season with higher amounts of suspended solids in the winter, and thus less transparency on average, and lower amounts of suspended solids in the summer, leading to more transparency on average. Secchi depths not only varied across seasons, but also by location in the lake. Secchi depths ranges average from about in the winter, depending on location in the lake, and in the summer. Secchi depths of have been recorded, indicating higher transparencies than average for the lake.

Lake Okeechobee is home to more than 40 species of native fish, along with introduced species, such as the Mayan cichlid, Cichlasoma urophthalmus. Fish species displaying varying distributions throughout the lake depending on seasonality, site depth, sediments, and turbidity. These fish populations support different wading birds, including various species of egrets, ibises, wood storks, and herons, along with alligator populations. Lake Okeechobee supports over 3,800 different arthropods, including insects and arachnids, along with around 400 species of nematodes.

Vascular macrophytes are important in the nutrient dynamics of lakes, along with creating micro habitats for fish and invertebrates, and providing substrate for epiphytes. Macrophytes provide the lake with oxygen through photosynthesis, along with acting as a buffer for eutrophication by uptake of phosphorus. However, with increased eutrophication of lakes along with climate change, trends are showing decreased richness of macrophytes. Because the fauna are so reliant on the macrophytes for habitat, food, and protection from predation, a decrease in macrophyte diversity and abundance has negative consequences on fauna richness. Macrophyte abundance is dependent on many abiotic factors such as water depth, water transparency and light availability, and nutrients, along with influence of biotic factors. Increasing phytoplankton and algal blooms from eutrophication and nutrient abundance can decrease water transparency and light availability to submerged macrophytes, providing one explanation how macrophytes are sensitive to eutrophication. Some submerged macrophytes that have been recorded at Lake Okeechobee include southern naiad (Najas guadalupensis), Illinois pondweed (Potamogeton illlinoensis), vallisneria (Vallisneria americana), and hydrilla (Hydrilla verticillata). The years 2005 and 2018 had particularly large volumes of water and TP inputs in relation to hurricanes increasing runoff. Despite limiting TP inputs by decreasing phosphorus use in agriculture, Lake Okeechobee has yet to reach the aimed target set by the South Florida Water Management District's in the 1980s of reducing the lake's TP by 40 μg/L. Although proposed by the South Florida Water Management District, this initiative of limiting the lake's TP to 40 μg/L was adopted by The Lake Okeechobee Technical Advisory Committee (LOTAC), the United States Environmental Protection Agency (USEPA), and the Florida Department of Environmental Protection (FDEP), but phosphorus inputs have yet to be controlled enough to reach this goal. In 2016, Lake Okeechobee experienced an extensive cyanobacteria algal bloom that lasted from May to mid July. During the previous 2015–16 winter, there were relatively high recorded temperatures, and higher than average rates of precipitation and storms in relation to the El Niño event. As mentioned, higher rates of precipitation can lead to greater influxes of runoff which unload more phosphorus into the lake, enabling harmful algal bloom. Along with this algal bloom in 2016, other algal blooms have been found to occur in relation to hurricanes and other climate events leading to increased water flow into the lake. Kramer et al. (2018) studied Lake Okeechobee during and after its major 2016 algal bloom that was related to the El Niño event. They collected information on nutrient availability, phytoplankton communities, and the presence of toxins, along with the genetic makeup of the phytoplankton communities and their genetic abilities to produce toxins. Additionally, they conducted nutrient experiments to couple with their findings. They found that cyanobacteria with the ability to do nitrogen fixation were in high abundance during this 2016 algal bloom. During this time, nitrogen was a limiting factor due to the extreme amounts of phosphorus in the freshwater ecosystem. The field experiments conducted with this study found that microcystin, the toxin produced by cyanobacteria, was produced in higher quantities when there was more nitrogen present.