Bacteria are everywhere, including in our surface waters. Most are harmless. Water resource managers test for the presence of certain bacteria in waterways to protect human health. Some kinds of bacteria may cause illness if people are exposed to them, and others are harmless but their presence may indicate contamination from sources that may contain other, harmful pathogens. The presence of bacteria can affect our ability to use surface water for drinking, swimming, and shellfish production and harvesting.
Bacteria come from a variety of sources, but those of most concern for human health come from the fecal waste of animals and people. Sources of fecal bacteria include:
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Malfunctioning septic systems
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Leaking sanitary sewers
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Confined animal feedlots / overgrazing
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Wastewater plant overflows
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Urban pet waste
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Wildlife
Water quality regulations identify the specific type(s) of bacteria used to indicate contamination from sources that may contain harmful pathogens.
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Enterococci typically are not considered harmful to humans but their presence in the environment may mean that the water is contaminated by fecal material and that other disease-causing agents such as viruses, bacteria, and protozoa also may be present. Enterococci are distinguished by their ability to survive in salt water and thus they are the preferred indicator of health risk in estuarine and marine environments.
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Fecal coliform bacteria are able to grow in elevated temperatures and are associated only with fecal material from humans and other mammals. While most are harmless the most common one, Escherichia coli (often abbreviated E. coli), can cause intestinal illness if ingested.
The maximum allowed number of these specific type(s) of bacteria in a waterway depend on the “designated use” of the waterway. Each waterway is assigned a “Class” which indicates how it is used by people.
The state water quality standards establish bacteria limits for each class.
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Class I waterways are sources of potable water, like reservoirs. Water quality standards require that they be tested for E. coli. Water drawn from Class I waters is treated to kill bacteria prior to distribution as potable water.
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Class II waters are used for shellfish propagation or harvesting. Water quality standards require that they be tested for fecal coliform bacteria (E. coli is one of these). In addition, the Florida Department of Environmental Protection (FDEP) uses the Florida Dept. of Agriculture and Consumer Services (FDACS) current open/closed shellfish harvest status report to determine impairment at the time of assessment, and any Class 2 waters that include "Prohibited" shellfish harvesting areas are deemed impaired for fecal coliform. ("SEAS Classification" is the stated reason for impairment). The FDACS water quality data itself is not included in the assessment and therefore, there may be waterbodies that are shown to be impaired for fecal coliform (SEAS Classification), although there are no data for fecal coliform available on the Water Atlas. For more information about shellfish assessment, refer to this document.
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Class III and Class III Limited* waters are used for recreation. Most waterways in Florida are Class III. For Class III waters, different bacteria rules apply for freshwater and saltwater. “Predominantly fresh” waters must meet water quality standards for E. coli, and “predominantly marine” waters must meet standards for Enterococci.
*Class III-Limited waters are similar to Class III, but have special water quality rule(s) applied to them because of exceptional environmental circumstances. These “Site Specific Alternative Criteria” are defined in Rule 62-302.800 of the Florida Administrative Code).
In addition to performing bacteriological testing required by the water quality standards, some water resource managers may test for other bacteria as well. These tests, and tests of other water quality characteristics, help in identifying possible source(s) of contamination.
