Mercury emitted from American smokestacks has been declining for years. But contamination levels in loons, walleyes and some other species have actually increased in the past decade, according to the largest report yet on mercury in the Great Lakes region.

The report, released Tuesday by the Great Lakes Commission, was based on 35 research studies and samples from tens of thousands of fish, birds and other animals. It concludes that the forests, lakes and wetlands that characterize the Great Lakes make the region particularly sensitive to mercury pollution.

Even more important, the authors conclude, the nature and extent of the region's mercury problem is more severe than was previously known -- and, for reasons that are not understood, appears to be getting worse for some species.

The report found that mercury levels are higher in fish in inland lakes than those in the big lakes. That was true of walleye from northern Minnesota and other heavily forested areas with wetlands.

Six of the 15 most commonly eaten fish had mercury levels higher than the EPA recommends for human consumption. And many species, including loons, showed sensitivities to mercury at much lower concentrations than had been known.

The report was released just as Congress is trying to block new standards by the Environmental Protection Agency that would cut mercury from coal-fired power plants, now the largest source of mercury. The U.S. House last week passed a bill to delay the regulations, which were expected to be finalized next month, because of concerns about their impact on the economy.

But mercury can inflict economic damage, too, the study's authors said. People who live in the eight Great Lake States consume more freshwater fish than those in any other region in the United States, they said. Sport fishing in those states supports more than 190,000 jobs and annually has an economic impact of more than $20 billion.

The commission is an inter-governmental agency that represents the eight Great Lakes states, Ontario and Quebec.

Mercury is a toxin that can be lethal to wildlife at high levels and, at lower levels can lead to reproductive problems. In humans, who consume mercury mainly through fish, it can affect brain development in children. It does not decompose, and, as a result, increases in concentration as it moves up the food chain, leading to fish advisory restrictions for children and pregnant women for some species of game fish.

It's been introduced into the environment since the 1800s by industrial processes, but the total amount has declined by 20 percent since the mid-1980s because of new regulations and technologies.

Bruce Monson, a research scientist with the Minnesota Pollution Control Agency who contributed research, said the rising levels in wildlife mean that for some reason they are taking up more of the mercury present in their environment. The trend may be more apparent in areas like northern Minnesota with many lakes and wetlands, because that's where exposure to certain bacteria makes mercury organic and bound up in the food chain.

Monson also said concentrations in walleye in northern lakes could be rising along with the higher average temperatures from climate change. The transformation of mercury into its organic form accelerates in warmer temperatures, he said.

Josephine Marcotty • 612-673-7394