Is it safe to swim at jordan lake?

We often get asked about the safety of water for body contact sports at presentations of our work to various groups and at our Facebook page.  The greatest concerns expressed are contamination by disease-causing organisms and algal toxins. Here is factual information about how water quality is tested in Jordan Lake and links for further reading.


EPA’s 2012 Recreational Water Quality Criteria are intended as guidance to states in developing water quality standards to protect swimmers from exposure to water that contains organisms that indicate the presence of fecal contamination.  The criteria specify:

  • indicator organisms to test

  • frequency of testing

  • estimated illness rate per 1,000 swimmers corresponding to the recommended

  • standard maximum value for indicator organisms

Indicator organisms are NOT harmful to human health. They only indicate the presence of fecal contamination.  Fecal matter of warm blooded animals, defined as mammals (humans included) and birds, may contain pathogens.  The organisms are bacteria, viruses and parasitic protozoa (e.g., that cause Giardia).  However, direct measurement of pathogens is extremely expensive and time consuming because there are so many agents and their identification is not always simple.


EPA conducted observational studies at seven beaches to support the 2012 Recreational Water Quality publication.  The results were used establish a relationship between the measured counts of selected indicator organisms and incidence rate of gastrointestinal illness. From this, the EPA published the following:


GM is the geometric mean of the number count of indicator organism measured as colony forming units (cfu) per 100 mL of water.  

The GM is a running average calculated by taking the nth root of the product of values.  EPA recommends weekly sampling. For instance, suppose we have 2 weekly results giving 10 and 30 cfu/100 mL.  The geometric means is square root (1/2 power) of (10×30) equal to 17.3 cfu/100 mL.

Now suppose that the third week’s result is 100.  The geometric mean is the cubic root (1/3 power) of 10x30x100 equal to 31.0 cfu/100 mL. This helps to capture the variability in time without giving undue weight to the last value.

The GM should not exceed the stated values shown in the table in any 30-day period. The STV is the statistical threshold value for the bacteria samples. It approximates the 90th percentile of the water quality distribution and should not be exceeded by more than 10 percent of the samples taken.


Bacterial counts change depending on what happens in the watershed.  Rainy weather, for instance, can cause the counts to increase very quickly. It flushes animal fecal matter off the land into rivers to produce a spike in indicator organisms. Suspended soil particles not only give rivers a muddy appearance after rains but they also allow attachment by bacteria, prolonging their survival time.

Rain also causes water to seep into sewer lines through poorly sealed joints.  If the carrying capacity of the sewer line is exceeded, raw sewage mixed with rain water will be bypassed into streams.  Failure of sewage pumping stations and too much sewage arriving at the wastewater treatment plant can also cause bypassing.  These events have occurred in the Jordan Lake watershed though usually limited to heavy rainfalls.

Weekly sampling is not enough to give 100% assurance to swimmers that the level  of indicator organisms is under the EPA published threshold.  Even hourly or daily sampling is still inadequate. This is because of the time delay in processing samples.  At least  24-48 hours are needed  to culture (grow) the sample in the laboratory before counting.

The North Carolina Recreational Water Quality Monitoring Program falls under the Shellfish Sanitation and Recreational Water Quality Section in the Department of Environmental Quality (DEQ). Coastal beaches are monitored but inland waters are not.  A two page brochure explains the state’s monitoring program in the form of Frequently Asked Questions and Answers and is recommended reading.

Directly relevant freshwaters like Jordan Lake is the following quote from the brochure:

QUESTION: Can I get sick from swimming in freshwater lakes and rivers?

ANSWER: Yes. Freshwater is affected by runoff and point source discharges just like coastal waters. Unfortunately, the state does not currently have a monitoring program for inland recreational waters. The public should avoid freshwater swimming after heavy rain, especially near storm drains.


All seven of the Jordan Lake State Recreation Area (JLSRA) beaches are within Chatham County. For the 2017 bathing season, Chatham County Public Health Department is voluntarily partnering with the JLSRA and the Chatham County Water Department to measure E. coli bacteria weekly at the beaches.  Their goal is to evaluate how rainfall and other factors affect bacteriological water quality of the lake.  They are following guidance set forth by EPA’s 2012 Recreational Water Quality document.

Lake water samples from the beaches are immediately brought to the laboratory at the Chatham County Water Treatment Plant for E. coli measurements.  Results are available in two days. CJL’s website will keep the public up-to-date on these results.

The chart below depicts results for first 15-weekly samples. The names of the seven beaches are shown in the legend.  In addition, total rainfall in the week preceding the sampling is indicated by the black dashed boxes and read from the scale on the right-side of the chart.  Note: there was no rain 1 week prior to Aug. 2, 8, 17, and 22 samplings.  The very high E. coli values seen in the June 21 and 28 samples could be caused by the fairly large rainfall amounts (2.4 and 1.3 in.) that preceded these samplings.  Sampling on July 6 was preceded by only a trace of rainfall and the E. coli returned to very low values.  With the exception of Seaforth Beach on July 18, 25 and Aug. 22 and Poplar Point on Aug. 8, the E. coli were barely measurable from July 6 to August 22.  Lack of rain for this period could explain these very low levels.


The geometric mean (GM) values of E. coli for the first 15-weekly samples in 2017 at each beach are given below.  All are well below 100 cfu/100 mL  (shown by red line) recommended by EPA to keep the illness rate below 32 per 1,000 bathers. This is despite several high values measured on June 21 and 28 (see chart above).  That’s because the GM is a running average so these few high E. coli values are dampened by the predominance of low E. coli values.  Nevertheless, to reduce your risk of bacterial illness, avoid swimming after heavy or prolonged rainfalls.


Results from the subsequent month of weekly samplings are not shown because all were less than 3 cfu/100 mL for E. coli and thus far below concern for swimmers.  The most likely explanation for such low values is no substantial rainfall since June.

Swimmer Precautions

Even though these bacterial measurements indicate a wide margin of safety for swimming, the following precautions are always recommended:

  • Don’t swim after a heavy rainfall

  • Don’t swallow the water

  • Rinse off after swimming



The local news media have carried many articles about the suspension of the Jordan Lake Rules which would have required taking measures throughout the watershed to limit phosphorus and nitrogen inputs so as to reduce the growth of algae.  Under strictly natural conditions,  algae are important members of a healthy food chain.  However, with excess nutrients, their levels become greatly elevated.  They become nuisance organisms causing taste and odors and depleting the water of oxygen during night hours, leading to fish kills.

Some types of bluegreen algae, more properly known as cyanobacteria, can also be a human health concern. In 2016, EPA issued guidelines and recommendations to protect recreational users from illnesses caused by cyanotoxins. The common illnesses are rashes, diarrhea, vomiting and breathing difficulty. In some cases, exposure to cyanotoxins can lead to liver, kidney and nervous system problems.  A companion EPA report details the gaps in knowledge, most notably limited health effects data and poorly understood exposure routes ( ingestion, inhalation and dermal).


Water samples are taken each month by the NC Department of Environmental Quality (NCDEQ) for measurements of the type of algae present and their cell density.  Several genus of bluegreen algae are known to dominate in Jordan Lake.  Their cell density is typically in the range of 100,000 to 300,000 units per milliliter 

According to  the algal ecologist for NCDEQ, dominance of bluegreens is common in many North Carolina lakes.  However, many genus do not produce cyanotoxins. The  genus Microcystis is responsible for the most common cyanotoxin.  This genus has not been identified in samples taken in  spring and summer of 2017 nor in past years. 


The Division of Water Resources (DWR) within NCDEQ has made available an Algal Bloom Map of the state.  This interactive GIS tool allows the viewer to look at locations where DWR took phytoplankton samples and analyzed for algal community composition density across the state.  Potentially harmful algal blooms (pHAB) are shown as red circles defined as blue-green (cyanobacteria) dominance in algal group having greater than 10,000 units per milliliter.  Of the 15 samples so far on map (2012-1016) at Jordan Lake, nine indicate pHAB.

In February 2018, a comprehensive scientific study entitled Algal Blooms and Cyanotoxins in Jordan Lake, North Carolina written by a research team from NC State University and NCDEQ was published in the Journal of Toxins.  It shows that multiple toxins were detected at 86% of the tested sites and during 44% of the sampling events between 2014 and 2016.  HOWEVER, concentrations were FAR BELOW levels set by the World Health Organization for safety of drinking water.  Nonetheless, the researchers caution that recurrence of multiple cyanotoxins provides impetus for more study.

At present, significant levels of Microcystis and other genus likely to produce cyanotoxins must first be identified by NCDEQ before the Environmental and Occupational Epidemiology branch in the Division of Public Health within the North Carolina Department of Health and Human Services will conduct a Health Risk Evaluation.  We must remain vigilant because the mix of algal species in a lake depends on many changing natural factors as well as nutrient input. 


Trash on the shoreline can also cause chemical pollution of the lake when the level rises after rainfall and inundates leaking containers of all types of residual fluids. For instance, our volunteers routinely find containers holding lubricants, hydraulic fluids, industrial adhesives, and gasoline along with an assortment of aerosol sprays, fire extinguishers as and pesticide spray applicators.

Any amount of chemical leakage can be considered as pollution.  However, the lake holds hundreds of billions of gallons of water.  Dilution of leaking containers by this huge amount of water probably makes it impossible to detect chemicals leaking out of containers amidst the shoreline trash with even the most sensitive of instruments. Nevertheless,  citizens should be concerned about any amount and type of pollution in a reservoir that supplies drinking water to 300,000.  Of course, we should add visual pollution to the list because it influences citizens’ perception of water quality, rightly or wrongly.