Preliminary NNC Calculator

Run New Calculation

Florida water quality standards use a combination of narrative and numeric criteria to determine whether water bodies are healthy. The narrative standards focus on whether an aquatic ecosystem is in balance by evaluating the abundance and composition of its plants and animals. The numeric standards support the narrative criteria by testing whether the levels of certain pollutants in a water body are causing environmental degradation by exceeding safe levels. The types of pollutants that are regulated include nutrients, metals, bacteria, pesticides, and other substances.

This Preliminary "Numeric Nutrient Criteria" (NNC) Calculator does a preliminary test of chlorophyll a, phosphorous and nitrogen levels in area water bodies, using data from water quality samples stored in the Water Atlas database, comparing their concentration to thresholds defined in the Florida Administrative Code (FAC). The intent of the Preliminary NNC Calculator is to informally evaluate recent nutrient levels in selected water bodies by comparing them to applicable state standards.

Nutrient pollution thresholds may apply statewide, regionally, or be water body-specific; they are defined in the FAC.

  • Thresholds for a lake depend on the amount of natural tannins it has, its alkalinity, its chlorophyll content, and its geographic region.
  • Thresholds for freshwater streams are determined by geographic region.
  • Many lakes and streams have water body-specific thresholds that supersede the statewide or regional standards.
  • At this time, thresholds have not been defined for tidally-influenced streams.
  • Each bay (estuary) has its own unique thresholds.
  • Some water bodies have pollutant thresholds that are expressed as nutrient loads (i.e., pounds per year) rather than as concentrations (e.g., milligrams/liter). Data for these water bodies are not evaluated by the NNC Calculator.

More detailed information may be found in the documents referenced in the "Related Links" section below.

The results produced by the Preliminary NNC Calculator are for information only and have no regulatory authority. They are not an assessment of waterbody impairment, which is done solely by the Florida Department of Environmental Protection, which continually collects and assesses water quality and biological data statewide to determine water quality and ecosystem impairment (https://floridadep.gov/dear/watershed-assessment-section).

Lake Numeric Nutrient Criteria (NNC) per Chapter 62-302.531 Florida Administrative Code
Long Term Geometric Mean Lake Color and Alkalinity Annual Geometric Mean Chlorophyll a Minimum calculated numeric interpretation Maximum calculated numeric interpretation
Annual Geometric Mean Total Phosphorous Annual Geometric Mean Total Nitrogen Annual Geometric Mean Total Phosphorous Annual Geometric Mean Total Nitrogen
≥ 40 Platinum Cobalt Units 20 ug/L 0.05 mg/L 1.27 mg/L 0.16 mg/L 2.23 mg/L
≤ 40 Platinum Cobalt Units and ≥ 20 mg/L CaCO3 20 ug/L 0.03 mg/L 1.05 mg/L 0.09 mg/L 1.91 mg/L
≤ 40 Platinum Cobalt Units and ≤ 20 mg/L CaCO3 6 ug/L 0.01 mg/L 0.51 mg/L 0.03 mg/L 0.93 mg/L
Stream Numeric Nutrient Criteria (NNC) per Chapter 62-302.531 Florida Administrative Code
Nutrient Watershed Region Total Phosphorous Nutrient Threshold Total Nitrogen Nutrient Threshold
Peninsular 0.12 mg/L 1.54 mg/L
West Central 0.49 mg/L 1.65 mg/L
Related Links
Numeric Nutrient Criteria Development Numeric Nutrient Criteria Implementation Lakes, Streams, and Spring Vents - Rule 62-302.531 Estuaries and Coastal Segments - Rule 62-302.532 Surface Water Quality Standards - Chapter 62-302, F.A.C. Identification of Impaired Surface Waters - Chapter 62-303, F.A.C.