Preliminary NNC Calculator

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).