In Canada, the toxic burden on communities near the tar sands is already enormous. In addition to direct human exposure, oil contamination in the local watershed has led to arsenic in moose meat—a dietary staple for First Nations peoples—up to 33 times acceptable levels. Deformed fish have been found in nearby Lake Athabasca; drinking water has been contaminated; and a huge swath of the vibrant Boreal forest is being transformed into a toxic moonscape. One of the largest dams in the world is restraining a giant reservoir filled with toxic sludge from processing tar sands into oil.

Processing tar sands oil means more asthma and respiratory diseases, more cancer, and more cardiovascular problems. Contaminated wastewater, containing arsenic, mercury and various carcinogens, has already been linked to elevated rates of cancer in downstream First Nations communities.

Greenhouse gas emissions
It takes around 3 times as much energy to produce a barrel of oil from tar sands as it does for typical oil extraction. (85.5kg CO₂ per barrel compared to 28.6kg CO₂). The expansion of oil sands is the fastest growing contributor to Canada's greenhouse gas emissions, yet the Canadian government is failing to regulate its carbon emissions effectively with absolute targets. Canada is set to miss its Kyoto targets.
Technological solutions such as carbon capture and storage are still years away, yet the companies are seeking licenses to increase carbon emissions at a time when the scientific community agrees the developed world needs to cut emissions.

Forests & Water
The oil sands reserves cover an area of 140,000km² of the boreal forest - equivalent  to 25 % of Alberta (approximately the size of France). The extraction of oil sands requires huge impacts above the ground with survey lines, mines, processing plants, pipelines and drilling sites. Oil sands mining has left swathes of forest removed, fragmenting the habitat of the native caribou. Companies have promised to restore the habitat, but only 104 ha of land has been certified as reclaimed.
Tar sands require from 2 to 4.5 barrels of water to produce a barrel of oil.  The Athabasca river cannot supply the quantities of water required for the proposed expansion, and the ecological viability of the river is already threatened.
The waste water is so toxic it has to be stored in tailings ponds that threaten leaks in to the river. Concerns have been raised by the First Nations indigenous communities that live downstream about serious health problems they fear are linked to contaminated water and fish.

Communities including the Athabasca Chipewyan, Mikisew Cree, Chipewyan Prairie Dene, Woodland Cree, Beaver Lake Cree, and Fort Mackay First Nations have all files lawsuits over runaway tar sands developments. failure to obtain free, prior and informed consent of these communities creates substantial material risks to continued developmentin the tar sands.