SOMBA K'E/YELLOWKNIFE - Mercury levels in some territorial lakes are so high the NWT's chief medical health officer has advised residents to eat fewer fish from the Deh Cho and Sahtu regions.

In a June 16 public health advisory, Dr. Kami Kandola recommended people stop eating predatory fish from Lac Ste. Therese, located about 100 kilometres from Deline, and from Cli Lake, which is about 115 km west of Fort Simpson, as those two lakes have more than double the amount of mercury Health Canada considers safe for average consumption.

Those eating fish from Trout Lake in the Deh Cho or Kelly Lake - about 30 km from Norman Wells - should try to eat smaller, younger fish only twice per week. Expectant mothers should eat only two servings a month and children aged five to 11 should have only 1.75 servings a month.

Organic mercury often makes its way into the ecosystem through naturally occurring sources in rocks, however it is also released into the environment when fossil fuels are burned. Mercury is toxic to the nervous system and in adults can cause numbness in fingers and feet, tremors, loss of vision or hearing, memory problems, seizures and brain damage. In small children even low levels of mercury can cause brain damage, learning disabilities and developmental problems.

Kandola said NWT residents should continue to eat fish, but should eat fish that are lower on the food chain since predatory fish amass more mercury in their bodies.

"To my knowledge, we've only seen high levels of mercury in adults who ate predatory fish every day as their main meal," she said.

Environment Canada collected the contamination data for these four lakes between 2006 and 2008. Russel Shearer, director of Northern Contaminants Program for Indian and Northern Affairs Canada (INAC), said most lakes and rivers in NWT are sampled and tested every five years, while Great Slave Lake and the Mackenzie River at Fort Good Hope are tested for contaminants every year.

"It is a high priority for us because we are concerned that some contaminants are reaching unexpectedly high levels in the Arctic ecosystem and people who have traditional diets are therefore exposed to these contaminants as well," Shearer said.

"We're monitoring the situation very closely with other federal departments, with the territorial governments, with the aboriginal governments in the area as well as the Northern communities themselves so we're doing this all together."

Lac Ste. Therese, in particular, has shown high levels of mercury since 1980, Shearer said. Mercury levels in fish from that lake have tripled since 1992 - average levels in walleye and lake trout were 3.5 and 2.3 parts per million, respectively, well above Health Canada's maximum safe consumption level of .5 ppm.

But not many people have been fishing there recently.

Deline resident Gordon Taniton said fishermen used to set nets at Lac Ste. Therese for pickerel and go ice fishing there by snowmobile in the 1980s, but fishing activity has waned since residents heard about the lake's mercury content.

"Usually they go over there for hunting, not for fishing," he said. "They don't have to worry about it because they don't go there."

The federal government began negotiations with other countries in the United Nations for a global mercury agreement June 7 in Stockholm, Sweden.

The UN aims to have an agreement in place by 2013 to cut down the world's mercury levels.