The Everglades, often called the “River of Grass,” is a massive subtropical wetland ecosystem stretching across southern Florida. This sprawling, shallow, slow-moving river flows from the Kissimmee River basin down to Florida Bay. The ecosystem is an internationally recognized biodiversity hotspot, providing habitat for over 360 bird species, the Florida panther, and the American crocodile. This mosaic of habitats, including sawgrass marshes, cypress swamps, and mangrove forests, is dependent on the natural flow and quality of its fresh water. Human impact has reduced the historic Everglades by nearly half, leaving the remaining ecosystem fragmented and imperiled.
Fundamental Alteration of Water Flow
The most significant threat to the Everglades is the physical disruption of its natural hydrology, which once supported the vast “sheet flow” of water. Beginning in the early 20th century, and accelerating with the 1948 Central and Southern Florida (C&SF) Project, extensive drainage and flood control efforts were implemented to reclaim land for agriculture and development. This massive engineering effort created a centralized network of over a thousand miles of canals, levees, and pumping stations.
This system compartmentalized the ecosystem, diverting approximately 70% of the water that historically flowed south, channeling it rapidly to the Atlantic Ocean and the Gulf of Mexico. The disruption starved the southern portions, including Everglades National Park, of the fresh water needed to sustain the natural wet and dry cycles. The restriction of this slow, natural flow has caused the ecological deterioration of vast areas, leading to the decline of wading bird populations and habitat fragmentation.
Contamination from Nutrient Runoff
The chemical composition of the Everglades’ water has been compromised by the influx of excessive nutrients. The Everglades is naturally an oligotrophic, or low-nutrient, system, with healthy phosphorus concentrations below 10 parts per billion (ppb). Runoff from agricultural areas north of the park, specifically the Everglades Agricultural Area (EAA), has historically contained high levels of phosphorus from fertilizer applications, sometimes exceeding 500 ppb.
This nutrient enrichment fuels the growth of non-native species, profoundly altering the food web. In areas impacted by the runoff, native sawgrass marshes are displaced by dense stands of invasive cattails. High phosphorus concentrations also cause the disappearance of periphyton, the community of algae and microorganisms that serves as a primary food source for invertebrates and fish, destabilizing the ecosystem.
Disruptions from Invasive Species
The ecosystem’s biological integrity is threatened by the introduction and proliferation of non-native species. The Burmese Python is the most notorious example, establishing a large breeding population after being introduced through the exotic pet trade and accidental releases. These large constrictors prey on a wide variety of native mammals, birds, and reptiles, including threatened species like the wood stork.
The python’s impact is evidenced by severe declines in native mammal populations within Everglades National Park. Studies have linked the proliferation of pythons to population drops of up to 99% for raccoons and opossums, and 87% for bobcats in certain areas. Invasive plant species, such as the Melaleuca tree, also pose a threat by outcompeting native plants like sawgrass, consuming large amounts of water, and altering the landscape’s natural fire regimes.
The Threat of Rising Sea Levels
Rising sea levels driven by global climate change pose a major danger to the Everglades, exacerbating problems caused by freshwater diversion. South Florida’s low elevation and porous limestone geology make it vulnerable to saltwater intrusion. As the ocean rises, saltwater moves inland, contaminating freshwater wetlands and the Biscayne Aquifer, a primary source of drinking water for millions of Floridians.
This encroachment has already caused the freshwater-saltwater transition zone to shift inland by at least a kilometer over the last half-century. The increased salinity stresses and kills freshwater-dependent vegetation, such as sawgrass, and causes the collapse of the organic peat soil that forms the marsh floor. Climate change is also intensifying the frequency and strength of tropical storms and hurricanes, leading to more extreme precipitation patterns that increase flooding risks and periods of drought and fire.
Current Efforts to Reverse the Decline
In response to decades of ecological decline, the Comprehensive Everglades Restoration Plan (CERP) was authorized by the U.S. Congress in 2000 as a large-scale, collaborative effort between federal and state governments. CERP is the world’s largest ecosystem restoration endeavor, covering an 18,000-square-mile area with the goal of restoring and preserving the South Florida ecosystem. The plan focuses on modifying the legacy infrastructure of the C&SF Project to re-establish the natural sheet flow of water southward.
Key objectives include capturing fresh water currently lost to the ocean and redirecting it to the environment, improving water quality by reducing nutrient loads, and increasing water storage capacity. Projects involve constructing reservoirs and Stormwater Treatment Areas (STAs) that use plants to naturally filter phosphorus before the water enters the Everglades. The aim of these efforts is to provide the correct quantity, quality, timing, and distribution of water necessary to sustain the ecosystem.