MADISON, Wis. – In olden days, Clarissa Welds, an elder of Lake Superior, as she calls herself, never worried about how many fish she ate.

“It was the way of our ancestors. We were fisherman, and Mother Earth gave us what we needed to survive. We didn’t have to worry if the food was safe,” said the Bad River Band of Lake Superior Chippewa Indians citizen.

“I miss those times.”

Welds’ outlook began to change after two children, one a relative and the other the child of a close friend, were diagnosed with learning disorders and behavioral problems in the 1990s.

Doctors said the health issues could have to do with their mothers’ diets, Welds recalls. Mercury in the freshwater fish they ate was a particular concern, according to medical experts.

Studies have shown the presence of mercury in food correlates with a variety of negative health effects, including the problems seen in the children close to Welds.

Health officials today say mercury, a neurotoxin, is still quite problematic. It is a persistent substance – one that doesn’t go away quickly or easily – that tends to affect the nervous system and is especially dangerous to pregnant women and youth.

The main source of contamination in natural waters is mercury that is released into the atmosphere and deposited into watersheds by precipitation. Coal-fired power plants are the largest source of mercury emissions in the United States.

In February, the Environmental Protection Agency announced that it intends to control air emissions of mercury from coal-fired power plants by issuing a rule under the Clean Air Act.

For now, the presence of mercury in lakes and streams doesn’t seem to be going away any time soon, despite stricter pollution monitoring and testing in many regions. In fact, new research from the Interior Department indicates that mercury contamination is widespread.

According to the department’s latest U.S. Geological Survey study, released in August, scientists detected mercury contamination in every fish sampled in 291 streams across the country. About a quarter of these fish were found to contain mercury at levels exceeding the criterion for the protection of people who consume average amounts of fish, established by the EPA.

Secretary of the Interior Ken Salazar said the science sends a clear message that the U.S. must continue to confront pollution, restore the nation’s waterways, and protect the public from potential health dangers.

Barbara Scudder, a USGS scientist, said the findings will help decision makers better manage mercury sources and better anticipate concentrations of mercury and methylmercury in unstudied streams in comparable environmental settings.

Welds was caught off guard because she knew the two mothers of the ailing kids ate well. Plus, she said, they weren’t obese, didn’t have diabetes, and seemed to have good nutrition habits.

One thing they had in common: They loved fish, especially trout. Welds had prepared it for both mothers on many occasions.

Since the diagnoses, the children and their mothers have gone on to live full lives, but haven’t eaten many fish, Welds said.

And neither has she.

Health experts say avoiding fish is one way to dramatically reduce the risk of mercury contamination and poisoning.

Many elders in recent years have become aware of the dangers of mercury contamination as a result of younger family members’ health issues, according to James Falcone, a wildlife expert from a Wisconsin-based conservation group.

“The message seems to get through to many older tribal members first. And they bring the message back to their kin and friends.”

Some tribal leaders are being proactive about getting the word out. The leadership of the Bad River Reservation issued a warning to the tribe about mercury contamination in 2004.

It also sent a letter to the leaders of the EPA, laying out its concerns about pollution and proposals that would affect mercury regulation in nearby waters.

“It is definitely good that tribal elders and leaders are taking the lead on this important matter,” Falcone said, “especially in light of the new scientific information.”

While the latest Interior data suggests many regions are already contaminated, there are areas that are far worse than others. Some of the highest levels of mercury in fish were found in the tea-colored or “blackwater” streams in North and South Carolina, Georgia, Florida and Louisiana.

High levels of mercury in fish were also found in relatively undeveloped watersheds in the Northeast and the Upper Midwest. Elevated levels were also noted in areas of the West affected by mining.

Complete findings of the USGS report, as well as additional detailed studies in selected streams, are available online.