Columbia -- New details of Lake Wateree fish contamination show cancer-causing PCBs were found in 65 percent of the fish tested by state officials last winter.

The study prompted state health regulators to warn people to limit the amount of largemouth bass, striped bass and blue catfish they eat from the lake, The State reported Wednesday.

Details released since show the extent of the contamination: The toxic PCBs were found in 22 of 34 fish examined, or 65 percent.

All 15 bass and four of five blue catfish tested positive for PCBs, according to records from the state Department of Health and Environmental Control. Three of 14 black crappie tested also had PCB contamination; state regulators said they still are safe to eat without limits.

Lake Wateree, about 30 minutes north of Columbia, is only the second reservoir in South Carolina to carry PCB health advisories. The reservoir also is the only major lake in central South Carolina's Catawba River basin to carry a PCB advisory.

"PCBs are a health concern," said David Merryman, the riverkeeper for the Catawba basin. "If they're found, especially in species like this that are caught for sustenance, it's an extremely salient issue."

PCBs, or polychlorinated biphenyls, are a class of industrial chemicals banned in the United States in the late 1970s because of the danger to human health, but they have lingered in the environment since.

The federal government considers PCBs probable human carcinogens. They have been linked to liver cancer in rats.

DHEC officials were not available to answer detailed questions about the PCB findings last week, agency spokesman Adam Myrick said. DHEC issued the health advisories last spring, but few media outlets reported on the problem. The agency has not yet posted signs warning the public about PCB contamination at Lake Wateree.

The agency's discovery has sparked concern among people who fish, swim and boat on the 13,000-acre lake that touches Fairfield, Lancaster and Kershaw counties. Some people have begun asking how the contamination occurred and whether it can be cleaned up.

So far, no one has the answer to either question, but PCBs are suspected of washing down the Catawba River from Charlotte, which dwarfs every other city in the river basin.

PCBs once were used as fire retardants and insulators for industry. They also were sprayed on dirt roads to help keep them from tearing up so quickly. Tainted dirt from road beds in the Catawba basin may have gotten into the lake, Merryman said, noting that PCBs bind to soil.

When PCBs reach waterways, they usually don't pollute the water itself, but settle in the mud on the bottom. Over time, fish slowly accumulate PCBs, often by eating small animals exposed more directly to the toxins.

"We recognize sediment is our number one pollutant, and it is carrying PCBs with it," Merryman said. "The more we develop land and increase storm water runoff, it exacerbates the sediment loading in our lakes and makes for the likelihood of increasing our PCB levels."

In addition to questions about industrial pollution, some workers dumped transformer oil containing PCBs at the lake in the 1940s to help control mosquitoes, The State reported in 1997. Information about the activity has been spotty, and the DHEC has not said what became of an investigation it conducted.

Although the DHEC's recent testing was limited and state regulators are still investigating, the agency's findings support recent federal concerns about PCBs in some Lake Wateree fish.

A 2009 federal report said Lake Wateree was one of just 17 percent of the nation's lakes with elevated levels of PCBs in certain fish. The U.S. Environmental Protection Agency study had documented PCB levels in largemouth bass that were six times higher than a federal health safety standard.

DHEC's study last winter followed up on the EPA report.

Records released by the DHEC indicate that the mean, or average, PCB level in largemouth bass, blue catfish and striped bass also exceeds the federal safety level cited in last year's report. The mean level of toxins in largemouth bass, blue catfish and striped bass were high enough to trigger the state warnings, records show.

The agency's fish advisory recommends that people not eat more than one largemouth bass per week and no more than one striped bass or blue catfish per month. Pregnant women and young children should not eat any of the fish, the agency said.