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Impaired Waters

What does this mean?

In Florida, a lake, river or stream is considered "impaired" if it fails to meet specific water quality standards, according to its intended use. For example:

Within each of these five 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.

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

How are the data collected? (Methods)

Many types of data are collected in efforts to determine whether or not a water resource is impaired. Some of the information is collected by state agencies, while other data are collected by trained volunteers.

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

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.

For more information, please refer to Florida LAKEWATCH Circulars.


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

An Edition of wateratlas.org