The federal government last year found a number of environmental issues related to the Alberta oil sands, including contaminant levels that exceed guidelines, higher-than-expected atmospheric concentrations of chemicals, and a lack of regional species such as marten and fisher.

Natural Resources Minister Greg Rickford was briefed by his department in January on an environmental monitoring report conducted on the oil sands last year.

The briefing note for the minister, obtained under access-to-information law, highlights some issues in the oil sands that environmentalists and First Nations have complained about for years and have used to call for a slow down or halt to oil-sands growth.

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"Naturally high erosion of sediment during the spring and summer or from rain caused metal concentrations in the Athabasca River and phosphorus and nitrogen in the water to exceed existing guidelines," the briefing note said, referring to contaminants probably resulting from the 2014 Alberta floods.

The briefing note relayed the findings of an oil-sands monitoring report issued jointly in mid-December by the federal and Alberta governments. The report is publicly available on a government website but was not previously reported on by news media.

The memo for Mr. Rickford said some wetlands water samples showed iron and cadmium concentrations that "exceeded established safe limits for aquatic life."

It said concentrations of contaminants called polycyclic aromatic hydrocarbons, or PAHs, in tailings pond water suggest their evaporation is leading to "a more significant source of atmospheric PAH concentrations than previously recognized."

PAHs can be released into the air, water and soil through the mining and processing of bitumen-rich oil sands, and their evaporation from tailings ponds was identified as an issue in early 2014 in a University of Toronto study.

While highlighting issues with contaminants and species at risk, the briefing note did not directly link environmental impacts to the oil sands, noting that "oil-sands-related pollutants in the environment are generally not at concentrations that give cause for concern." It added: "Although some pollutants exceeded existing guidelines, no evidence has been uncovered that directly links these to oil sands development."

Amin Asadollahi, oil sands program director at the Pembina Institute, a think tank, said the briefing note does not serve the minister well.

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"It's quite concerning that the federal government is aware of but continues to downplay environmental impacts of oil sands," Mr. Asadollahi said. "It's time for the federal government to acknowledge impacts of oil sands on the environment, enforce its own rules, and ensure that the sector is actually developed in a responsible manner."

Jacinthe Perras, a spokeswoman for Natural Resources Canada, said in a statement that the government is supporting technological innovation to improve oil-sands environmental performance.

The federal and Alberta governments are working together to deliver a "comprehensive, integrated, world-class environmental monitoring system for the oil-sands region," she said.

Environmentalists and First Nations have criticized oil-sands projects for seepage and leakage of chemicals from tailings ponds, affecting communities downstream.

Alberta's Athabasca Chipewyan First Nation is fighting new pipeline constructions as it draws attention to oil-sands contaminants found in water and in hunted animals such as muskrat and moose.

Wildlife that prefer old forest habitat, such as marten, fisher and bay-breasted warbler, "were found to be less abundant in the oil-sands region than would be expected in an undisturbed area," the briefing note added.

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Environmentalists have been similarly drawing attention to a shrinking caribou population in the oil-sands area. Mr. Asadollahi said there are close to 90 species at risk in the region.

Greg Stringham, vice-president of oil sands and markets for the Canadian Association of Petroleum Producers, said oil producers work under rigorous monitoring by the Canada-Alberta Joint Oil Sands Monitoring program (paid for mostly by industry), the Alberta Environmental Monitoring, Evaluation and Reporting Agency, as well as the Alberta Biodiversity Monitoring Institute.

"We think the tailings ponds are actually safe and working the way they're supposed to," Mr. Stringham said, adding that the oil producers are planning reclamation of the ponds as mines are finished. "The reason we do all that monitoring is to have the very earliest indication that might require a change in behaviour."

Last October, Mr. Rickford told oil and gas executives in a private strategy meeting in Banff, Alta., that they need to do more advocacy of oil-and-gas projects, conduct environmental research and collaborate more with aboriginal communities.

"You are fighting an uphill battle for public confidence," Mr. Rickford's speaking notes said, according to documents obtained by Bloomberg through access-to-information. He added: "Our messages are not resonating."

The new NDP government in Alberta under Premier Rachel Notley pledged in its campaign to strengthen environmental standards in the province.

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The party platform said an NDP government would step up "monitoring and enforcement to protect Alberta's water, land and air. We will build standards based on independent science and international best practices."