Yes, salmon. The heart-healthy fish that's also supposed to make you smarter stands accused of causing cancer. A study published in Science magazine last month says that salmon raised on farms in the U.S. and Europe has higher levels of pollutants than salmon caught in the wild. It recommends eating farmed salmon just once a month.

There are a number of fishy things about this study, starting with the fact that the proven health benefits of eating salmon far outweigh the risk of cancer. In response to the report, the Food and Drug Administration says that "consumers need not alter consumption of farmed or wild salmon at this point in time." Britain's food watchdog agency also rose to salmon's defense, saying the levels of pollutants reported in the study are within internationally recognized safety limits.

The Science study found trace amounts of polychlorinated biphenyls (PCBs) in farm-raised salmon. But PCBs aren't proven human carcinogens. Long-term studies of factory workers exposed to high levels of PCBs show that there is no increase in the incidence of cancer. Moreover, contaminant levels in salmon have gone down 90% in the past 30 years.

But even if PCBs were a danger, they wouldn't pose a threat in the quantities in which they are found in farm-raised salmon. The Science study found the concentration of PCBs to be 1.8% of the level the FDA finds tolerable--an average of 36.6 parts per billion compared with 2,000 parts per billion in the FDA's guidelines. Put this in perspective: If a person eats eight ounces of farmed salmon every week for 70 years, the PCBs would increase his cancer risk by one in 100,000, the Environmental Protection Agency says.

Avoiding salmon can actually be bad for public health. Salmon is packed with omega-3 fatty acids, which are proven to reduce heart attacks. Studies indicate that the omega-3 in salmon may also be vital to brain development in young children and fetuses, help fight Alzheimer's, and help prevent breast cancer.

The Science study has had one predictable effect. Two environmental groups in California this month announced their intention to sue 50 companies in the U.S., Canada and Europe--from salmon farms to grocery giants Safeway and Albertsons. The Environmental Working Group and the Center for Environmental Health plan to bring suit under a state law requiring companies to alert customers if their products contain dangerous levels of chemicals known to cause cancer. These groups can't win their battles on the scientific merits in Congress, or even in such friendly bureaucracies as the EPA, so they are increasingly turning to the courts.

Now that salmon has been discovered by greens and trial lawyers, who knows what kind of wild ride we're in for. But one thing is clear: The latest salmon scare isn't about nutrition or food safety.