Population growth and alterations of south Florida's major watershed by drainage and development have had severe environmental consequences. About 40 percent of the water that originally flowed from Lake Okeechobee into the Everglades is now diverted directly to the Gulf of Mexico by the Caloosahatchee Canal and to the Atlantic Ocean by the St. Lucie Canal. Saltwater intrusion into freshwater aquifers has extended as far as six miles inland from the coast in some areas. Lowered water tables have resulted in oxidation of drained peats and damaging peat fires, which have lowered the land surface three to six feet in 60 years in some agricultural areas.

Scientists checking water quality.

Regional water quality has been degraded. Water pumped into canals from agricultural lands can have high concentrations of nutrients, insecticides, herbicides, and fungicides. Nutrients in water are necessary for productive aquatic ecosystems, but in high concentrations they can damage aquatic life and human health. The high nutrient concentrations and loads entering Lake Okeechobee and the Everglades from farms and cattle lands have increased lakewide phosphorus concentrations two and one-half times over the past 15 years and massive algae blooms have become more frequent and persistent. The increased nutrient loading to the northern Everglades is stressing the existing vegetative communities.

In residential and urban areas, septic-tank drainfields are a source of nutrients and of potential bacterial contamination. Stormwater runoff from urban areas commonly carries heavy metals, nutrients, bacteria, viruses, and pesticides. Urban runoff and discharge of inadequately treated, nutrient-rich effluent into canals have resulted in some canal waters becoming covered with algae and choked with aquatic weeds. Ground water in the highly urbanized Atlantic Coastal Ridge in the southeastern part of the study unit is highly vulnerable to contamination from surface sources because the highly permeable Biscayne aquifer allows rapid infiltration of surface waters. Drainage and development also could be implicated in the contamination of fish and wildlife by mercury. Health adversaries warn the public against eating fish from the Everglades because of mercury contamination, the source of which is still under investigation. Florida Bay also has undergone environmental changes during the past 10 years that are unprecedented in the period of recorded observations. Seagrasses have died over large areas of the bay, algae blooms have increased in frequency and duration, and fisheries have declined. These changes have been attributed to a variety of causes, including altered freshwater and nutrient inflows from the watershed.