Actress Daphne Zuniga
Nutritionally, fish may seem like your friend. But the mercury in many fish can cause everything from miscarriage and heart problems in adults to mental retardation in babies. Actress Daphne Zuniga, who was lucky enough to get early treatment, spotlights the growing threat.

Tuna on Rye—Hold the Mercury, Please
I'm one of the most health-conscious people I know. I do yoga, meditate, hike, run. I don't eat meat, so fish has been my primary source of protein. Tuna on Caesar salad—you can't beat that for lunch. And yellowtail sushi—clean, nutritious, melt-in-your-mouth yummy. Every time I grilled fish or ordered it at a restaurant, I felt I was making a healthy choice.

Then late last year, after learning about the risk of mercury poisoning with a high-fish diet, I got tested. Just for the heck of it; I didn't expect problems. When the doctor told me my numbers were double the normal, "safe" level of mercury, I thought there was a mistake—didn't she know how healthy I was? I asked about the symptoms of mercury poisoning. Muscle aches, I was told, plus blurred vision, depression, inability to concentrate, memory loss, skin rashes. As I listened, I thought, check, check, check.

About 6 percent of women of childbearing age have levels of mercury above those deemed safe by the Environmental Protection Agency. That means their unborn children are at risk for mental retardation, learning disabilities and impaired hearing.

Mercury is a potent brain poison. How does so much of it get into our bodies? Industrial pollution—from coal-burning power plants and chemical factories—deposits toxins in our rivers, lakes and oceans, where they're ingested by fish. Twenty-one states have consumer advisories on all their freshwater lakes and rivers, according to the Environmental Protection Agency, meaning that their fish are too poisoned to eat regularly. The American Medical Association recommends that a mercury warning be posted wherever fish is sold, but I've never seen one anywhere.

Find out how you can protect yourself. You can even print out a guide to make better choices when buying or ordering fish.