Mercury levels in fish are on the rise in some locations after years of decline in Ontario lakes, according to researchers from the University of Toronto. Because the province covers a wide geographical area that contains about one-third of the world’s fresh water, the findings, they say, may reflect changes on a large scale. Mercury levels in fish are on the rise in some locations after years of decline in Ontario lakes, according to researchers.

Cutting to the chase, while this information may create alarm, especially for pregnant women fearing mercury poisoning for unborn infants, none of the lakes offered in the Wilderness North destinations reported high levels of mercury. This is mostly true due to their remote locations far from mining or lumbering operations believed responsible for some the mercury increases.

While the researchers found an overall drop in mercury since the 1970s, levels are creeping back up at more than half of locations sampled, especially in Ontario’s most northern lakes.

The researchers collected data on more than 200,000 fish collected by the Ontario Ministry of the Environment over the past 40 years. The samples included fillets from game fish from nearly 3,000 locations.

The percentage of locations showing a flat or increasing trend for mercury in walleye increased from 29 percent in the 1970s and 1980s to 59 percent between 1995 and 2012. During that same period, the locations showing increasing mercury for pike rose from 44 percent to 73 percent.

The researchers also found an increase in places with fish containing more than .61 micrograms of mercury per gram – the level at which the Ontario Ministry of the Environment advises against eating more than four fish meals per month from a given area. (The advisory level for pregnant women and children is much lower.)

It’s not clear why mercury levels in fish are on the rise, while airborne emissions are down. Similar upwards trends have been seen in some lakes in Minnesota and parts of the Great Lakes.

“Other factors, such as global emissions, climate change and invasive species are likely affecting the response,” wrote the researchers.

Canada’s weather also has been warmer over the past 60 years. Warmer lakes make mercury more mobile and accelerate the rate that fish accumulate mercury. Mercury levels in fish in northern Ontario lakes were increasing at a greater rate than levels in southern Ontario fish.

These trends “suggest a mixed positive/negative outlook for the North American environmental mercury problem,” the researchers concluded.