The state Division of Public Health officials said Wednesday that large mouth bass and catfish in Badin Lake have had elevated PCB levels.
The lake is located east of Charlotte in Stanly and Montgomery counties.
Alcoa Inc, which operates an aluminum plant near the lake admits, it is likely responsible for the contamination.
A smelter or metal melting factory that is also owned by Alcoa, but is no longer in operation, is also located on Badin Lake.
In addition to those facilities, Alcoa operates four electric-generating dams on Yadkin River that feed Badin Lake.
According to published reports, Alcoa said its smelter, on the lake's southern shore, probably contaminated the lake's sediment.
However, investigators say two of the contaminated fish came from the lake's northern end.
Health officials believe the PCBs may have traveled by air and Alcoa says they may have come from upstream.
"We need to try to do more investigation of where those [chemicals] are coming from," said John Dorney, a division official in charge of water-quality certification. "The public's going to want to know where this stuff is coming from."
PCBs are chemicals formerly used as coolants and transformer lubricants that were released into the environment through manufacturing or improper disposal and storage of electrical equipment.
The fish have been under mercury advisories since 2006.
Pregnant or nursing women or children under 15 are advised not to eat from the lake. Others should not eat more than one weekly meal including fish from the lake.
Badin Lake is the third North Carolina body of water where consumers were warned about eating fish contaminated with PCBs. The other two lakes are near Raleigh.
North Carolina regulators are required to certify that the company's operations won't harm water quality in the Yadkin River in order for Alcoa to renew its 50-year federal hydroelectric license. The state has until respond by May.