[3] Okeechobee covers 730 square miles (1,900 km2) and is exceptionally shallow for a lake of its size, with an average depth of only 9 feet (2.7 metres).

They called the lake Mayaimi, meaning "big water", as reported in the 16th century, by Hernando de Escalante Fontaneda.

[9] Slightly later in the 16th century, René Goulaine de Laudonnière reported hearing about a large freshwater lake in southern Florida called Serrope.

[9] By the 18th century the largely mythical lake was known to British mapmakers and chroniclers by the Spanish name Laguna de Espiritu Santo.

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".

[15] In both cases the catastrophe was caused by flooding from a storm surge when strong winds drove water over the 6.6-foot (2-meter) mud dike that circled the lake at the time.

[citation needed] The organization was authorized to cooperate with the U.S. Army Corps of Engineers in actions to prevent similar disasters.

[citation needed] The 1947 Fort Lauderdale Hurricane sent an even larger storm surge to the crest of the new dike, which was expanded again in the 1960s.

Hurricane Ernesto increased water levels by 1 foot (30 cm) in 2006, the last time it exceeded 13 feet (4.0 m).

Over a seven-day period (including some storms that preceded Fay), about 8 inches (20 cm) of rain fell directly onto the lake.

According to tests from the South Florida Water Management District, arsenic levels on the northern part of the lake bed were as much as four times the limit for residential land.

During this time, portions of the lake bed, covered in organic matter, dried out and caught fire.

[18] In late August 2008, Tropical Storm Fay inundated Florida with record amounts of rain.

Lake Okeechobee received almost a 4 feet (1.2 m) increase in water level, including local run-off from the tributaries.

[22] The outbreak was possibly due in part to nutrient-laden waters reaching the lake from farms and other sources.

The Florida Department of Environmental Protection and Martin County had carried out toxicity testing on the algae, but had not funded any work to clean up the water, and a FEMA spokesman said that "The state has robust capability to respond to emergencies and disasters.

Lake Okeechobee sits in a shallow geological trough that also underlies the Kissimmee River Valley and the Everglades.

Although daily thermal stratification is brief, a hypolimnion can form during this time resulting in decreased amounts of dissolved oxygen at the lake bottom.

Secchi depths of 1.7 metres (5.6 ft) have been recorded, indicating higher transparencies than average for the lake.

The Army Corps of Engineers targets keeping the surface of the lake between 12.5 and 15.5 feet (4 and 5 m) above sea level.

[45] Fish species displaying varying distributions throughout the lake depending on seasonality, site depth, sediments, and turbidity.

[33] Yearly fish recruitment was found to be positively correlated with increased water levels, providing more substrate and protection.

[44] Fish diets in Lake Okeechobee depend on macro-invertebrates and zooplankton,[44] such as calanoids, cyclopoids, and cladocerans.

[citation needed] 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.

Algal blooms like this can be harmful to the environment, including the lake's flora and fauna, because of released toxins.

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.

[55] As mentioned, higher rates of precipitation can lead to greater influxes of runoff which unload more phosphorus into the lake, enabling harmful algal bloom.

[56] Kramer et al. (2018) studied Lake Okeechobee during and after its major 2016 algal bloom that was related to the El Niño event.