Charlotte Harbor is a 270-square-mile estuarine system in west-central Florida. It is being subjected to increasing environmental stress by rapid population growth and development. Population in the inflow area may double by the year 2020, resulting in increased demands for freshwater and increased waste loads.

The Myakka, Peace, and Caloosahatchee Rivers are the major rivers emptying into the harbor. About 70 percent of the land in these three river basins is composed of agricultural land and rangeland. In the coastal basin around Charlotte Harbor, about 50 percent of the total land area is devoted to commercial or residential uses. Water use in the inflow area is about 565 million gallons per day, of which 59 percent is used for irrigation, 26 percent for industry, 11 percent for public supply, and 4 percent for rural supply.

Total freshwater inflow from the three major rivers, the coastal area, and rainfall directly onto Charlotte Harbor averages between 5,700 and 6,100 cubic feet per second, which is more than 3,500 million gallons per day. A trend analysis of about 50 years of streamflow data shows a statistically significant decreasing trend for the Peace River stations at Bartow, Zolfo Springs, and Arcadia. There is no significant trend in the Myakka or Caloosahatchee River data. In the Peace River, the decrease in flow may be related to a long-term decline in the potentiometric surface of the underlying Floridan aquifer system, which resulted from ground-water withdrawals. It is not possible to determine whether the trend will continue. But if the trend does continue at the same rate, except for brief periods of storm runoff, the Peace River at Zolfo Springs could be dry year-round in about 100 years.

There are 114 facilities permitted to discharge domestic or industrial effluent to waters tributary to Charlotte Harbor, of which 88 are in the Peace River basin. Phosphate-ore and citrus processing account for most of the industrial effluent. Several locations in the headwaters of the Peace River have been significantly affected as a result of receiving wastewater effluent. The Peace, Myakka, and Caloosahatchee Rivers transport more than 2,000 tons per day of dissolved solids, more than 17 tons per day of nitrogen, and about 6 tons per day of phosphorus.

By the year 2020, the population in the inflow area is expected to increase by more than 500,000 people, which will require an additional 76 million gallons per day for water supply. The increased population will produce an additional 60 million gallons per day of domestic wastewater resulting in an additional 3 tons per day of nitrogen and 0.65 ton per day of phosphorus. More than 150 square miles of land will be converted to urban uses, producing another 0.25 ton per day of nitrogen from urban runoff. These increased nutrient loads can be expected to occur concurrently with decreased freshwater inflow.