Elevated levels of mercury have been detected in Oregon bass, prompting health officials to warn residents against eating too much of the fish.

The Oregon Health Authority issued a statewide advisory Tuesday after evaluating tissue samples from 62 bass from 11 water bodies across the state, including the Columbia, Snake, John Day, Grande Ronde and Owyhee rivers. Results showed mercury at high enough levels to pose a threat to human health if not eaten in moderation.

Samples were collected between 2008 and 2014. The advisor affects bass from all waters in Oregon, and will remain in effect for the foreseeable future.

Bass are the focus of concern because they are a resident species — that is, they live in the same place their entire life, unlike salmon and steelhead. Bass are also top predators, eating other contaminated fish within the ecosystem.

OHA is recommending the general population eat no more than six meals worth of bass per month. A meal is about the size and thickness of your hand. Pregnant and nursing women, infants and children are at higher risk of mercury, and should eat no more than two meals per month.

That being said, Dave Farrer, toxicologist with the OHA Public Health Division, said fish are still an important part of a healthy diet. While the advisory is meant to keep people informed, it is not meant to take all fish off the table.

“The elevated levels of mercury we’re talking about in bass are of concern to us, but there are some simple steps people can take to reduce their exposure to mercury when consuming bass,” Farrer said.

People who eat too much fish with too much mercury can suffer organ damage and problems with their nervous and reproductive systems over time. Babies and small children can also develop life-long learning or behavior problems if exposed to high levels of mercury.

According to OHA, mercury can be harmful to human health if it exceeds .6 milligrams per kilogram of fish, or .2 milligrams per kilogram for those most vulnerable. The average total concentration of samples ranged from .8 to .86 mg/kg of mercury.

Lonnie Johnson, conservation director for the Oregon Bass Angler Sportsman Society, previously said most bass fishermen are catch-and-release only. However, the state did recently lift bag limits on all warmwater species, including bass, on the Columbia, John Day and Umpqua rivers.

Should more data become available, OHA said it will update advisories as necessary. All statewide fish advisories are posted online at www.healthoregon.org/fishadv.

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Contact George Plaven at gplaven@eastoregonian.com or 541-966-0825.