St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District
St. Johns River Water Management District -

Water bodies, watersheds and storm water
Green Cove Spring main view

Green Cove Spring main view

Green Cove Spring

Clay County


Green Cove Spring is a third-magnitude spring on the west bank of the St. Johns River. A concrete railing measuring 2 feet high with a diameter of about 15 feet encircles the main vent of the spring pool. The pool tapers downward as an irregularly shaped funnel into soft marl to a 2-foot-diameter cavern opening in its bottom, approximately 30 feet below the pool surface. The 2-foot vent then opens into a cavern 25 feet wide, trending in a northeast direction toward the St. Johns River. The roof of the cavern descends to a depth of 50 feet, and the bottom of the cavern falls to 98 feet (Rosenau et al. 1977). In August and September 2010, divers from Karst Environmental Services reported that the deepest penetrable point in the cave system was at 98 feet. The divers reported that all of the flow was coming vertically, from deeper depths.

Green Cove Spring vent

Green Cove Spring vent

Discharge from the spring pool is through a 4-foot-wide weir opening on its northeast side to a 50-foot by 100-foot swimming pool. The swimming pool overflows through a weir on its east end to a spring run that flows about 450 feet eastward to the St. Johns River. Some or all of the flow from the spring can be directed from a flume to bypass the swimming pool. The spring is part of a city-owned park and recreation area, with picnic tables, benches, walkways, and shade trees.


Green Cove Spring run

Green Cove Spring run

Discharge at Green Cove Spring was measured by the U.S. Geological Survey (USGS) seven times from 1929 to 1972. St. Johns River Water Management District measured discharge 54 times from 2000 to 2010 and currently measures discharge six times per year. From 1929 to 2010, the difference between the minimum and maximum discharges is 3.8 cubic feet per second (cfs). The maximum measured discharge of 5.4 cfs occurred in February 1929; the minimum discharge of 1.6 cfs occurred in March 2000. The mean and median discharges for the period from 1929 to 2010 are 2.94 cfs and 2.82 cfs, respectively (see the table below).

Green Cove Spring Discharge Graph
Discharge Graph

Water quality

Green Cove Spring was sampled by USGS seven times from 1956 to 1989. The district sampled Green Cove Spring 40 times from 2000 to 2010 and currently samples the spring four times per year. Summary statistics of the water quality data for selected variables are shown in the table below.

Green Cove Spring Water Quality Graph
Water Quality Graph

Summary statistics of water quality and discharge at Green Cove Spring

Green Cove Spring Min Mean Median Max Count Period
Discharge, cfs 1.57 2.94 2.82 5.40 61 1929−2010
Alkalinity, total, mg/L as CaCO3 77.7 84.8 82.0 170.0 43 1956−2010
Calcium, total, mg/L as Ca 25.0 27.9 28.0 29.3 40 2000−2010
Chloride, total, mg/L as Cl 4.8 6.0 6.0 8.7 45 1956−2010
Dissolved Oxygen 0.15 0.15 0.15 0.15 1 2001
Fluoride, total, mg/L as F 0.20 0.26 0.27 0.30 13 2000−2003
Magnesium, total, mg/L as Mg 13.0 14.8 15.0 16.0 39 2000−2010
Nitrate + nitrite, total, mg/L as N 0.00 0.02 0.01 0.04 9 2001−2009
Orthophosphate, total, mg/L as P 0.00 0.02 0.01 0.04 7 2001−2008
pH, field 6.92 7.87 7.91 8.81 46 1956−2010
Phosphorus, total, mg/L as P 0.00 0.01 0.01 0.03 7 1972−2010
Potassium, total, mg/L as K 1.2 1.5 1.5 1.9 40 2000−2010
Sodium, total, mg/L as Na 4.1 4.5 4.5 5.6 40 2000−2010
Specific conductance, field, µmhos/cm at 25°C 223 282 290 332 39 2000−2010
Specific conductance, lab, µmhos/cm at 25°C 261 285 284 326 34 1956−2010
Sulfate, total, mg/L as SO4 44.5 52.5 53.1 58.0 45 1956−2010
Total dissolved solids, mg/L 152 181 178 223 42 1957−2010
Water temperature, °C 23.5 24.7 24.7 25.9 43 1960−2010
Units: µmhos/cm = micromhos per centimeter
         mg/L = milligrams per liter
         cfs = cubic feet per second

Age of discharge water

The age of water discharging from Green Cove Spring was determined by measuring the concentration of tritium, delta carbon-13, and carbon-14 in the spring discharge, which was measured in March 2001. Green Cove Spring did not have any tritium, which suggests that the water is old. Green Cove Spring had a delta carbon-13 value of −7.32 parts per thousand and a carbon-14 concentration of 5% modern carbon. The Fontes and Garnier (1979) carbon-14 age is 14,397 years old.


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St. Johns River Water Management District
4049 Reid Street, Palatka, FL 32177
(800) 725-5922