TORONTO - If the huge trout you caught from one of the Great Lakes ends up on your dinner table you might be at risk from alarmingly high levels of toxins, says a new report from advocacy group Environmental Defence.

And at least four years of government data shows the condition of the fish isn't improving, according to the report released Friday.

"It's something so subtle. You're not going to eat a piece of fish and suddenly get cancer," said Mike Layton, Environmental Defence program manager and one of the report's authors.

"Like the fish, it's going to accumulate in your own body."

The report, "Up to the Gills," focuses on toxic chemicals in Great Lakes fish by examining advisories published by the Ontario Ministry of Environment for eight species of fish in 13 locations across the Great Lakes.

Many fish were found to be partly or completely unfit for human consumption, with bigger fish being the worst for a meal. The toxins in the fish included mercury from coal-fired power plants, dioxins from industrial processes and pesticides.

Some species of fish around the Toronto area need to be avoided entirely, the report found. These include lake trout and large carp. Even small fish with lower levels of contaminants should only be consumed in certain amounts, said Layton.

The report also analyzed advisories from 2005 to 2009 and found that the condition of fish was not improving. Fish from the water bodies like Lake Superior had the lowest contamination level while Lake Ontario was the worst.

But that doesn't mean people should forego fish altogether.

"We just want people to be careful about where their fish comes from," Layton said.

A provincial publication -- the Guide to Eating Ontario Sport Fish -- was central to providing the report's data. The guide, which is published every other year, gives consumption advice for species tested in waterways across Ontario. The advice is based on health protection guidelines from Health Canada.

Layton said the guide, while useful, may not be getting into the right hands. Making the guide more accessible and distributing it to targeted groups who fish in problem spots is an important step that needs to be taken, he said.

Tackling the source of the problem by reducing pollution from industry, sewage systems, agriculture and urban run-off into the Great Lakes was also recommended.

The report also urged federal and provincial governments to update the Canada-U.S. Great Lakes Water Quality Agreement. The agreement, which was signed in 1972 to protect and restore the Great Lakes, has not been revised since 1978.

"We need to take immediate action, we need stronger government action," Layton said.

Ontario's Ministry of the Environment will examine the recommendations made by the report, said spokesperson Kate Jordan.

"We are a world leader in monitoring contaminants in sport fish," said Jordan, adding that the provincial consumption guide has specific advice for children and childbearing women.

The guide is available at numerous locations including bait and tackle shops, select liquor store outlets, Ontario travel offices, provincial parks and the ministry's website, said Jordan.

A generally stable trend has been noted for consumption advisories in Great Lakes fish, Jordan said. Releases of mercury into the Lakes have also declined by 88 per cent since 1988, she added.

The province has invested in upgrading five sewage treatment plants in Ontario as well as remediation of sediment in the Hamilton Harbour, among other efforts, said Jordan.

"We know there is more work to be done, that's why we're prepared to providing funding to clean up hot spots in the Great Lakes," she said.

Things may not be as bad as they seem, said the Ontario Federation of Anglers and Hunters.

"We don't want to send out the 'sky is falling message.' There's a lot of good news that's being overshadowed here," said the federation's fisheries biologist Jeremy Holden.

Significant clean-up efforts around the province's lakes have left them in better shape than before, said Holden.

"There are a lot of healthy fish in the Great Lakes and a lot that provide unbelievable angling opportunities," he said. "We don't want to take the worst-case scenario and paint it across the province."