2.7.9. Doctors Lake

2.7.9.1. About Doctors Lake

Figure 2.38 The Doctors Lake Tributary (WBID 2389 and 2410).
Figure 2.38 The Doctors Lake Tributary (WBID 2389 and 2410).
  • West of the St. Johns River in Clay County
  • Primary Land Use: Forested
  • Current TMDL reports: Nutrient (2389), DO/Nutrient (2410),         Silver (2389/2410), Mercury
    • 2016 Verified Impairment for Nutrients (Chlorophyll-a and Total Phosphorus 2389)
    • WBID Area: 8.4 sq. mi.
    • Beneficial Use: Class III F

2.7.9.2. Data sources

Data were downloaded from the FL STORET and WIN websites (DEP 2010f; DEP 2018c) and filtered based on the stations (DEP 2010g) in Doctors Lake WBIDs 2389 and 2410 (DEP 2014c) shown above. The filtered dataset reflects water column concentrations and was used to generate Table 2.10, with freshwater stream WQC’s reported. These should be regarded as guidelines only because Swimming Pen creek (2410) is accessed as a stream, Doctors Lake (2389) is accessed as a lake and has different WQC’s.

2.7.9.3. Discussion

Water quality data for Doctors Lake are shown in Table 2.10. A final TMDL report to address nutrients and dissolved oxygen within this tributary has been published (Magley 2009e). The average total phosphorus concentration has exceeded the WQC for colored lakes (0.05 mg/L) the past three years. Average dissolved oxygen levels are well above the SSAC. Doctors Lake has been identified as being impaired for nutrients (chlorophyll-a and total phosphorus) (DEP 2016j). Recent water samples continue to show elevated phosphorus concentrations, and average chlorophyll-a levels were higher than the WQC in 2017 and 2019.

SJRWMD completed a demonstration project to remove TP from treated wastewater effluent entering Doctors Lake, and the project is expected to begin operation in the 2019-2020 fiscal year.  At full scale, SJRWMD reports that this additional treatment will remove approximately 6,500 pounds of phosphorus annually (SJRWMD 2020f). There were also plans in the 2019-2020 fiscal year to switch 79 residences in Clay County from residential septic systems to the central sewer system, resulting in an estimated decrease in TN loading of 1,486 pounds annually (SJRWMD 2020f).

Elevated maximum arsenic, cadmium, copper, nickel, silver, and zinc concentrations were previously measured in Doctors Lake, and as a result, EPA has published a Silver TMDL (EPA 2010a). Doctors Lake is largely used for recreational activities such as boating, fishing, and waterskiing. These activities could account for some of the copper, nickel, and zinc contamination; however, the source of the other contamination is not clear. Recent data show that concentrations of these contaminants have remained roughly steady over the past three years.

No recent measurements were available in WIN or STORET from 2016 to 2018 for the following parameters:

  • Fecal Coliform

Historical water quality data for Doctors Lake are available in previous versions of the River Report.

Table 2.10 Water quality data for Doctors Lake.

 Water QualityAverage and Number of Samples º
ParameterCriteria (FW)201720182019
Dissolved Oxygen (mg/L)≥34% sat. (≥3.0)7.90
(1 of 20 samples)
6.23
(4 of 28 samples)
6.86
(1 of 16 samples)
Total Nitrogen (mg/L)<1.54Not availableNot available1.13
(3 of 23 samples)
Total Phosphorus (mg/L)<0.050.07
(7 of 14 samples)
0.10
(15 of 16 samples)
0.09
(23 of 25 samples)
Chlorophyll-a (µg/L)<20117.02
(5 of 8 samples)
14.63
(3 of 8 samples)
37.65
(13 of 23 samples)
Arsenic (µg/L)≤502.40
(0 of 6 samples)
2.75
(0 of 8 samples)
1.78
(0 of 12 samples)
Cadmium (µg/L)≤0.30.06
(0 of 6 samples)
0.03
(0 of 8 samples)
0.02
(0 of 12 samples)
Copper (µg/L)≤9.30.95
(0 of 6 samples)
2.75
(0 of 8 samples)
4.82
(1 of 12 samples)
Lead (µg/L)≤3.2Not available0.54
(0 of 8 samples)
0.35
(0 of 12 samples)
Nickel (µg/L)≤520.22
(0 of 6 samples)
0.56
(0 of 8 samples)
0.54
(0 of 12 samples)
Silver (µg/L)≤0.070.00
(0 of 6 samples)
0.06
(1 of 8 samples)
0.01
(0 of 12 samples)
Zinc (µg/L)≤1201.29
(0 of 6 samples)
2.50
(0 of 8 samples)
3.33
(0 of 12 samples)
Fecal Coliform (CFU/100 mL)<400Not availableNot available240
(1 of 8 samples)
Turbidity (NTU)<29Not available4.38
(0 of 7 samples)
5.07
(0 of 12 samples)
Note: Hardness-dependent freshwater criteria for cadmium, copper, lead, nickel, and zinc were generated based on a hardness concentration of 100 mg/L.
° = Number of samples below Water Quality Criteria for Dissolved Oxygen; Number of samples above Water Quality Criteria for all other parameters.
FW = freshwater; SW = saltwater (marine). Values denoted with (*) indicate a proposed criterion, which has not yet been adopted.
Values denoted with (‡) are reference values based on EPA criteria (EPA 2010b), but the water body is not regulated by this standard.