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A study by the Alaska Department of Environmental Conservation found high enough levels of mercury in five species of fish to trigger the guidelines.

Women who are or who could become pregnant, children under 12 years old and nursing mothers should limit their consumption of large halibut and lingcod, yelloweye rockfish, spiny dogfish and salmon shark to one to two times a week, according to the guidelines. These people also should limit their consumption of store-bought and restaurant halibut, which average 33 pounds, to four times a week.

The department encouraged all other people, including men, teenage boys and women who cannot become pregnant "to consume as much fish from Alaska waters as they want."

The health department emphasized the benefits of eating fish and said those "far outweigh any potential risk from the small amounts of contaminants found in most Alaska fish."

The study sampled more than 2,300 fish among 23 species of fish sampled from Alaska waters between 2001 and 2006.

All the species contained some level of mercury, but levels in Alaska salmon are very low, the statement said.

The main source of mercury is air emissions from power generation and other industrial and waste disposal activities, according to the Environmental Protection Agency. Mercury naturally occurs in coal and is vaporized by coal-fired power plants. Mercury makes its way into waterways, and large fish that eat other fish tend to have higher levels of the heavy metal.

• Amanda Fehd can be contacted at amanda.fehd@juneauempire.com.