French Broad at Pearson BridgeE. coli Estimator
The E. coli estimator is valid from May to September. See you next swim season.
The E. coli estimator is valid from May to September. See you next swim season.
An estimated exceedance of the primary or secondary value does not indicate a closure or advisory but is meant to inform the public that there may be an increased risk based on current river conditions. It is always advised the public follow DHHS guidelines when recreating in natural waters found here. More detailed information about the estimator and E. coli in river systems can be found under the FAQ section.
Primary Recreation: Activities that include full immersion in the water and where potential exists for ingestion such as swimming and snorkeling. E.coli values greater than 126 MPN represent an increased exposure risk for primary recreation.
Secondary Recreation: Activities where there is lower or limited potential of full immersion and ingestion of water such as tubing and kayaking. E.coli values greater than 886 MPN represent an increased exposure risk secondary recreation.
What is E. coli?
E. coli, a type of fecal coliform, is a diverse species of bacteria found in the environment, food, and intestines of animals and humans. The presence of E. coli at elevated levels in streams, lakes, and rivers is an indication of potential point and nonpoint source pollution. Click here to visit the U.S. Environmental Protection Agency’s (EPA) website for more information on nonpoint sources. While most strains of E. coli do not cause disease, their presence at elevated levels can indicate potential fecal contamination, which has been shown to co-occur with gastrointestinal illnesses. The EPA has determined that E. coli is the preferred fecal indicator bacterium to use when evaluating for health advisories in freshwater.
About the E. coli Estimator:
E. coli is a fecal indicator bacteria and is used to determine human health risks from waterborne pathogens. The FBR E. coli estimator provides near real-time estimates of E. coli levels at Pearson Bridge in the recreational corridor of the French Broad River in Asheville, North Carolina. Having near real-time estimates is useful, as E. coli levels can increase rapidly over minutes, hours, or days during and following rainfall runoff events in the watershed. The estimator relies on the relationship between E. coli and turbidity at Pearson Bridge. If turbidity is known, E. coli may be estimated. This is important because E. coli sampling and analysis is time and labor-intensive, while turbidity can be measured instantaneously. The U.S. Geological Survey operates and maintains a gauge at Pearson Bridge which records turbidity measurements every 15 minutes, and the E. coli estimator uses these data to provide an estimate of E. coli levels at this location only.
How does the E. coli Estimator compute an estimated E. coli value?
Studies at Pearson Bridge have shown a close relationship between E. coli and turbidity (the amount of cloudiness in the water). Based on this relationship, a log-linear regression equation was developed to estimate E. coli based on a turbidity value. The estimate is meant to describe conditions at Pearson Bridge. It is common in all waterbodies for E. coli to increase as turbidity increases, so elevated turbidity and E. coli at Pearson Bridge is an indication that other turbid sections of the French Broad River would be expected to contain elevated E. coli as well. The estimator is not intended for use beyond the area of Pearson Bridge. Future studies will evaluate whether a similar estimation model may be appropriate for other sections of the French Broad.
The log-linear regression model used in the E. coli Estimator is as follows: Estimated E. coli = 10^[1.22333 + (1.09065*Log Turbidity)] * 1.24. The model produced an r2 = 0.75 and a RMSE = 0.28. For purposes of this web portal, the range of estimator error is defined as plus or minus one standard deviation (= 0.29, log scale) from the estimated value. The likelihood of the estimator’s upper range under predicting the actual E. coli value is ~16%, which represents the false negative error rate).
What is the source of E. coli in the French Broad River (FBR)?
While a portion of the E. coli in the FBR is associated with periodic, unpermitted discharges (e.g., sanitary sewer overflows, spills, etc.), the primary sources of E. coli are often from nonpoint source pollutants such as urban runoff, agricultural runoff, livestock in streams, pet wastes, wildlife wastes, failing septic systems, etc. E. coli also lives and reproduces in bed sediment and in surface waters with elevated sediment and nutrient loads which, at times, are present in the FBR. Analytical methods, though costly, exist to identify the species (i.e., humans, cows, dogs, birds, etc.) associated with the source(s) of E. coli pollution. These methods may be used strategically and in conjunction with continued E. coli monitoring to better understand and ultimately reduce the sources and locations of bacteria pollution in the FBR.
What is the Division of Water Resources (DWR) doing in response to the E. coli present in the French Broad River?
The DWR Asheville Regional Office (ARO) has recently established a program to better understand and report E. coli in the FBR recreational corridor and other watersheds in the region. A primary goal of the program is to evaluate different approaches to data collection, evaluation, and risk communication, and to partner with other agencies and stakeholders who are interested in E. coli impacts on recreational rivers, associated health risks, and recreational advisories. ARO has been monitoring E. coli in high-use recreational segments of the FBR near Asheville since May 2019 and is now evaluating additional monitoring in other highly recreated stream segments in Western North Carolina. The data collected so far have been used to better understand the relationships between variables most often associated with elevated bacteria (E. coli) such as rainfall, flow, turbidity, temperature, etc. This has culminated in a real-time log-linear regression model that estimates E. coli based on turbidity at the Pearson Bridge section of the FBR.
While DWR continues to address point source bacteria through its regulatory permitting programs, it is now strengthening its efforts to identify and address nonpoint bacteria sources through several collaborative projects with local stakeholders. Nonpoint source pollution, unlike the rigid regulatory framework for point source pollution, is addressed through federal grant programs referenced in the Clean Water Act under section 319(h). The programs fund local entities in developing and implementing nonpoint source management programs such as watershed restoration plans. Click here for more information on North Carolina’s 319 program.
What can be done to reduce E. coli levels?
To address nonpoint E. coli sources in watersheds, robust and well-funded partnerships are needed that engage state, county, municipal, commercial, environmental, and citizen stakeholders. Remedies to reduce or eliminate these sources exist (e.g., enhanced infrastructure, implement best management practices on agricultural operations, increased use of permeable surfaces in urban areas, improved stream buffer strategies, more effective nutrient management, improved stormwater capture, etc.), but all require support and action at the citizen level. There are many ways to become involved. For example, ensure your property is not contributing to sediment or chemical (i.e., fertilizer) runoff; support a watershed coalition to develop a watershed action plan; let your government representatives know you value the state’s rivers, lakes, and streams; support funding for restoration efforts and protective approaches at the local, state and federal level; and others.
Where can I find additional information or report a water quality issue?
For information on current recreational advisories, please contact your local health department. If you observe excessive foam, sheen, discoloration, or other changes in water quality, please contact DEQ at 1-800-858-0368, or the Asheville Regional Office during business hours at 828-296-4500.
Where can I find additional information regarding health risks?
For information regarding the health risks associated with swimming in natural waters or additional information pertaining to how the recreational values were obtained, please contact DHHS at 919-707-5900 or OEEB@dhhs.nc.gov.
The E. coli estimator is a collaborative project between DEQ’s WNC Recreational Monitoring Program and MountainTrue supported by funds from Pigeon River Fund, and supporters of MoutainTrue.