Similar consumption advisories were issued for Santeetlah Lake and Fontana Reservoir in 2011.
David Yow, a fisheries biologist for the N.C. Wildlife Resources Commission, said mercury is present in most fish, but some have higher levels than others.
"You have to make a point of having fewer meals of those fish with higher levels," he said, explaining that large predator fish such as walleye and bass tend to have much higher levels of mercury than smaller species.
Health officials said that consumption of fish targeted as high-mercury risks should be limited to no more than one meal per week for adults. Children and nursing mothers are advised not to eat possibly contaminated fish.
High mercury levels also have an adverse effect on all fish species, affecting schooling and spawning success.
While the exact source of mercury contamination is not known, the U.S. Environmental Protection Agency says the largest source of pollution comes from coal plants and coal-fired boilers.
In 2011, the EPA set new standards for air pollution, placing limits on the amount of mercury released from coal-fired plants. The regulations also include reducing acid gas, lead, nickel and arsenic emissions.
To determine mercury levels in fish, samples are collected by Commission biologists and analyzed by the N.C. Division of Environment and Natural Resources. Epidemiologists at the N.C. Division of Public Health then decide if advisories should be issued.