Last month, for the first time in about 15 years, Kentucky changed its fish consumption advisories.

There are high levels of mercury in most of the commonwealth’s lakes and rivers. But there is a conflict between what state agencies are saying and what they’re doing: On one hand, the state is warning people not to eat large amounts of fish because it contains the toxic chemical. On the other, state agencies are suing the federal government over pollution controls that would keep mercury out of waterways in the first place.

Kentucky regulators made the decision to tighten the advisory because they have more data now than in the past. Over the last few years, increased monitoring of lakes and rivers showed higher levels of mercury and polychlorinated biphenyl, another environmental toxin, in the water.

Statewide, the general population is advised to not eat more than one predatory fish from a Kentucky waterway per month, and no more than one bottom-feeder fish per week. The standards are stricter for children and pregnant women.

So, how does mercury get into the fish in the first place?

“Two-thirds of all airborne mercury is from the smokestacks of coal-fired power plants,” said Garrett Stillings, who works in the Kentucky Division of Water.

The mercury comes out of the smokestacks into the air, and eventually falls into the water. There, it bioaccumulates through the food chain. As big fish eat smaller fish, their tissue absorbs more and more mercury. And it’s that fish-tissue mercury that’s potentially harmful when it’s eaten by people — especially vulnerable people, like children and pregnant women.

Fish consumption advisories are common around the country, and regulators agree they’re an important tool. If you have a pollution problem that could cause harm to people’s health, you should warn them about it.

But it’s a reactive way to deal with a significant pollution problem: rather than focus on cleaning up the pollution, change behavior to avoid exposure.

“This is bad stuff, and we should be doing everything we can to prevent it from entering the environment,” said Kentucky Waterways Alliance Director Judy Petersen. “The thing is, of course, that Kentucky is very against new air regulations that would control some of the mercury and other toxins that are emitted from the coal-fired power plants.”

Kentucky was one of 20 states that sued the Environmental Protection Agency over its Mercury and Air Toxics Rule, which puts stricter emissions requirements on power plants. Last year, the Supreme Court sent the rule back to a lower court, saying the EPA hadn’t considered the additional costs to utility companies early enough in the process.

Regardless of how the rule ends up, Kentucky’s energy landscape is changing in a way that will likely help reduce the amounts of mercury in local rivers and streams.

Several of the state’s power plants have shut down in the past few years or announced plans to do so soon. And while, in general, the mercury that ends up in local fish is probably partly from local and regional sources and partly from overseas, scientists have found correlations between reducing U.S. emissions and local mercury levels.

Other than controlling power plant emissions so less mercury gets into the air in the first place, there are few other options for cleaning up waterways — and fish — once they’ve been contaminated with mercury.

Division of Water environmental scientist John Brumley said the only real solution is time.

“It’s just not an easy fix,” he said. “Getting those air emissions down would be one thing, but getting it flushed out of the system is another.”

Eventually, mercury in rivers will wash downstream. And if it’s not replaced by new sources of mercury, over time, fish will contain less of the toxin.

Petersen said she’s happy regulators are alerting Kentuckians about the mercury problems in the state’s lakes and rivers, but there’s a lot more that could be done.

“We shouldn’t be like, ‘there’s nothing we can do,’” she said. “There are things we can do. And again, this is not something that we can turn on and off, so we need to do all we can to control it.”

In the meantime, Stillings of the state Division of Water said the fish consumption advisories aren’t meant to scare people away from eating Kentucky fish.

“We’re not saying ‘do not eat these fish.’ Fish are a good source of protein, a good source of Omega 3’s,” he said. “We encourage people to eat the fish from Kentucky waters.”

Just check out the fish consumption advisory before you do.