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Impaired Waters

What does this mean?

The federal Clean Water Act (CWA) requires states to identify waters that do not or are not expected to meet applicable water quality standards with current pollution control technologies alone.

A lake, river or stream is considered "impaired" if it fails to meet specific water quality standards, according to its classification and intended use. These classifications are spelled out in section 62-302.400 of the Florida Administrative Code.

Within each of these categories, water managers rely on a variety of data to determine if the water resource has been impaired. To make this determination, they study the creatures living in the water resource (e.g., algae, bacteria, plants and wildlife) along with water chemistry and physical characteristics such as water clarity and/or turbidity.

The administration of the Impaired Waters Rule has been delegated to the State of Florida by the U.S. Environmental Protection Agency. Enforcement of the Rule is performed by the Florida Department of Environmental Protection (FDEP).

A statewide data summary is available in the 303(d) Report which is compiled and updated every two years by the FDEP. The state's minimum water quality criteria (or standards) are available in Chapter 62-303 of Florida's Administrative Code (FAC) as part of the Impaired Waters Rule (IWR).

The FDEP’s Watershed Assessment Section is charged with evaluating surface water quality, in order to determine whether a water body is meeting the applicable standards.

The FDEP uses a five-step watershed-based management cycle:

  1. Preliminary Assessment – Produce a “Planning List” and “Study List” for each Basin Group (group of watersheds). Each Basin Group is assessed every 5 years.
  2. Targeted Monitoring and Listing – Monitor water bodies, verify their impairment, and adopt a “Verified List” of water bodies to be legally designated as “impaired” by a particular pollutant. (This list is equivalent to the 303(d) list.)
  3. Develop and Adopt Total Maximum Daily Loads (TMDLs) – A TMDL document specifies an allowable pollutant load for a water body, group of water bodies, or watershed, and allocates parts of the total pollutant load to point sources and nonpoint sources which include both anthropogenic (human-caused) and natural background sources of the pollutant.
  4. Implement TMDLs – FDEP works with stakeholders to develop pollutant reduction plans to bring levels of pollutants below regulatory limits. To meet pollution reduction targets, a Basin Management Action Plan (BMAP), Reasonable Assurance Plan (RAP) or other implementation plan approved by DEP may be used.
  5. TMDL/BMAP Implementation – Stakeholders undertake the actions defined in the pollutant reduction plan and monitor water quality to assess the effectiveness of those actions.

Water bodies are continually monitored and assessed, both by FDEP and by stakeholders that include county and city governments. Monitoring and assessment are performed to determine the degree to which water quality standards are being met. Monitoring may include biological, chemical, and physical measures of water quality, fish tissue and sediment sampling, land use data, predictive models, and surveys.

A TMDL document contains the scientific determination of the maximum amount of a given pollutant that a surface water can contain and still meet the water quality standards that protect human health and aquatic life. Water bodies that do not meet water quality standards are identified as "impaired" for the particular pollutants of concern - nutrients, bacteria, mercury, etc. — and TMDLs must be developed, adopted and implemented for those pollutants to reduce pollutants and clean up the water body. (TMDL documents created by the EPA for Florida waterbodies exist and technically are still in effect, although the expectation is that the FDEP will create new TMDLs that supersede them.)

Pollutant reduction plans, whether a BMAP or another management tool, should do the following:

* There is also a "Class III Limited" designation for waters with human-induced physical or habitat conditions that, because of those conditions, have limited aquatic life support and habitat that prevent attainment of Class III uses.

How are the data collected? (Methods)

Many types of data are collected in an effort to determine whether or not a water resource is impaired. Sampling is conducted by the FDEP Watershed Assessment Section, supported by environmental scientists employed within individual FDEP Districts.

Biological data includes information about algae, bacteria, plants and other wildlife:

You can find Biology Reports by using the FDEP's Bureau of Laboratories Report Search tool.

Water chemistry data are also obtained from in-situ (i.e., within the water) and lab analyses of surface water samples. This often includes analyses for various forms of nitrogen and/or phosphorus—two essential nutrient groups found in virtually all water bodies.

Physical characteristics such as water clarity and/or turbidity and suspended solids are measured. Good water clarity is necessary for light penetration into the water column, allowing aquatic plants to photosynthesize. The amount of oxygen dissolved in the water is measured; both plants and animals that live in water require oxygen for respiration.

Water chemistry/physical data can be found in the FDEP Watershed Information Network (WIN) database (2017 and later) and/or in the Storage and Retrieval (STORET) database (2017 and earlier). WIN and STORET are the source of much of the data displayed on the Water Atlas websites.

The core function of the Watershed Assessment Section is to use the best available information to identify waterbodies and water segments (WBIDs) that are not meeting the applicable water quality standards and designated uses based on the Impaired Waters Rule Chapters 62-303 and 62-302, Florida Administrative Code.


See Atlas data.

Caveats and Limitations

It is important to note that even if some of these values exceed state standards, it doesn't necessarily mean a water resource is impaired. Water quality characteristics may vary considerably from one sampling event to the next in response to changes in weather conditions, stream flow, and many other variables. Scientists look for significant changes over a period of time, before they consider the waterbody impaired.

This approach of identifying and prioritizing impaired waters is part of the Clean Water Act of 1977 and also the 1999 Florida Watershed Restoration Act. As a result of these legislative acts, science-based pollution limits, called Total Maximum Daily Loads (TMDLs), are being developed to promote the clean-up of each and every impaired waterway.

For more information about impaired waters and the standards being used to evaluate them, read:

Additional Information

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