When they caught the sickly fish, each taken from a different part of the lake, the two Indigenous men immediately figured that it had something to do with the massive tar sands oil mines that lie about 300 kilometers upstream along the Athabasca River. “We have been putting two and two together, and raising concerns about the fast pace of [tar sands] development,” Chief Adam told me in a phone interview this week. “The tailing ponds are leaking and leaching into the rivers, and then going downstream to Lake Athabasca.”Here in the United States, public opposition to the tar sands has centered on the proposed Keystone XL pipeline: how it could jeopardize the fresh water supplies of the Ogallala Aquifer and how it would increase greenhouse gas emissions by keeping us locked into the petroleum infrastructure. For now, those worries remain hypotheticals. But for the people of Ft. Chipewyan — a community of about 1,200 that is only accessible by plane most of the year — the environmental impacts of the tar sands are already a lived reality. According to a 2009 study by the Alberta Cancer Board, the cancer rate in Ft. Chipewyan is higher than normal. Many of the residents there blame the industrial development south of them for the disproportionate cancer rates.

The deformed fish caught two weeks ago included a northern pike that had lesions along its back and belly and a sucker that was missing many of its scales. Chief Adam says the strange fish are so worrisome because the majority of Ft. Chipewyan residents still rely on traditional foods, including fish from the lake, to eat.

Chief Adam sent the two fish to the labs of the Canadian Cooperative Wildlife Health Centre in Alberta for testing. It will take biologists there several weeks to determine the cause of the deformities.

This isn’t the first time that sickly fish have been pulled from Lake Athabasca. In September 2010, the Ft. Chipewyan band released photos of fish that were also lesion-covered.

The Athabasca Chipewyan First Nation are one of the most active and outspoken critics of the tar sands development. In 2011 the tribe filed a suit against Shell Oil Canada for failing to uphold agreements it had made for two of its open pit mine projects. Chief Adam has said that his tribe may follow the example of the Beaver Lake Cree and challenge proposed tar sands projects on the grounds that increased mining could violate the tribe’s treaty rights to practice hunting and fishing.

“They keep building and building, and something has to give,” Chief Adam says. “And it’s the environment down here in Lake Athabasca. We want answers before we want further development. If they won’t give us answers, we will give them further resistance.”