The Everglades is a vast, subtropical wetland in South Florida, characterized as a slow-moving, shallow expanse of water covering a limestone shelf. The sheer size and unique topography of this ecosystem mean that the water depth constantly changes across both time and distance. Because of these natural fluctuations, there is no single, fixed answer to how deep the water is in the Everglades.
Defining the “River of Grass” and Average Depth
The defining characteristic of the Everglades is its legendary “sheet flow,” which earned the region the nickname “River of Grass.” This massive, slow-moving body of fresh water historically flowed from Lake Okeechobee south toward Florida Bay. This broad, shallow flow could be as wide as 50 miles, moving across the landscape at an almost imperceptible rate, sometimes as slow as 100 feet per day.
For most of its immense area, the water depth is remarkably shallow. The average depth across the main marshlands is generally less than one foot (0.3 meters). In many areas, the water is only a few inches deep for much of the year. This extremely shallow depth is a direct result of the nearly flat, subtle gradient of the limestone bedrock, which slopes southward at only about two inches per mile.
Factors Causing Seasonal and Geographic Fluctuation
The depth of the water is primarily dictated by the region’s seasonal climate, which includes a wet and dry cycle. The wet season, which typically runs from May through October, is when the ecosystem receives about three-quarters of its annual rainfall. During this period, the influx of water from heavy rains and Lake Okeechobee runoff causes water levels to rise significantly across the marsh.
The dry season, lasting from November to April, sees a dramatic drop in water levels due to reduced rainfall and high rates of evaporation. This seasonal shift means that areas that were inundated during the summer may dry out completely by late winter. The overall depth is a dynamic measure, increasing rapidly with the onset of summer rains and receding gradually throughout the cooler months.
Geographic features also create significant variation in water depth across the landscape. Deeper channels, known as sloughs, like the Shark River Slough, act as the main drainage pathways for the sheet flow. These sloughs can reach depths of up to three feet (one meter) during peak wet season conditions.
Conversely, the expansive sawgrass ridges and marl prairies are much shallower. Sawgrass ridges are often only barely covered with water, or they may become entirely exposed during the dry season. This difference of just a few inches in elevation between the ridges and the sloughs creates the patterned “ridge and slough” topography unique to the Everglades.
Water Depth as the Key to Ecosystem Health
Slight differences in water depth are fundamental to the health and structure of the Everglades ecosystem. The duration of flooding, known as the hydroperiod, governs which plant communities can survive in a given location. For example, tall sawgrass thrives in areas that are seasonally flooded but eventually dry, while cypress trees and mangroves are adapted to different water depths and salinity levels.
Water levels also directly influence the reproductive success of the region’s wading birds, such as the wood stork and the white ibis. During the transition into the dry season, receding water concentrates small fish and aquatic prey into smaller pools and sloughs. This concentration of food is a necessary trigger for successful nesting, providing the easily accessible food required to feed their young.
If water levels remain too high during the nesting season, the prey remains dispersed, which can lead to nesting failure for the bird colonies. Conversely, if the water dries too quickly or too early, the concentrated prey base may be depleted before the nesting cycle is complete.
Human Control and Water Management
The Everglades is heavily influenced by an extensive system of human-engineered controls. Beginning with the Central and Southern Florida Project (C&SF) authorized in 1948, a network of canals, levees, and pumping stations was built primarily for flood control and water supply. This project compartmentalized the ecosystem, converting vast areas into Water Conservation Areas and largely replacing the natural sheet flow with controlled, channeled flow.
Water managers actively adjust the water levels within these compartments, often creating unnaturally deep pools in some areas while over-draining others. This management can override the natural seasonal fluctuations that historically defined the ecosystem. The Comprehensive Everglades Restoration Plan (CERP), authorized in 2000, is the world’s largest effort to restore a natural flow regime by reestablishing the historic volume, timing, and distribution of water.