Pollution sources

In the river’s lower basin (that portion of the river flowing north from Welaka to the river’s mouth at Mayport), many human activities unintentionally add nitrogen and phosphorus to surface waters. Urban development, farming and industry have all contributed to the river’s decline.

Factors threatening the health of the lower St. Johns River include man-made pollutants, such as partially treated sewage from our homes and businesses, as well as from industrial sources, which is pumped into the river for disposal.

In the lower basin, treated wastewater is the largest contributor of nutrient pollution. In everyday terms, wastewater is partially treated sewage created by all of us, which is transported by underground pipes to a wastewater utility’s plant for treatment and disinfection. Then, in many cases, the wastewater is pumped into the St. Johns River for disposal.

Other major nutrient pollution sources include farms in the tri-county agricultural area of Flagler, Putnam and St. Johns counties. Agricultural runoff from farming areas take animal wastes, fertilizers and pesticides into the waterway through canals, ditches and streams that lead to the river.

Storm water from urban and suburban areas also pollutes the river. Runoff from metropolitan and developed areas sends lawn fertilizers, sediments, pesticides, roadway grease and trash into the river and its tributaries.

Long ago, before the land was developed, Florida was an area with numerous wetlands, also known as swamps or marshes. But development by humans has led to the destruction, filling in and paving over of wetlands, which are important ecological systems. Wetlands help filter out pollutants and sediments collected by storm water as it runs over the earth’s surfaces before reaching fragile waterways. Wetlands also provide habitat for organisms and serve as stormwater control systems by controlling flooding.

In addition to increasing flood risks, development has led to increased pollutants and sediments in stormwater runoff. Fertilizers and pesticides, motor oil and heavy metals wash off lawns, sidewalks, streets and parking lots with rainfall or excessive irrigation. Storm water contributes 80 to 95 percent of the heavy metals — copper, lead and cadmium — that enter Florida waters.

The upstream watersheds of the upper and middle St. Johns River also contribute significant amounts of nitrogen and phosphorus to the lower basin.