Obed Mountain coal mine spill

The Obed Mountain coal mine spill was a mining disaster that occurred on October 31, 2013, when a waste pit at the Obed Mountain Mine failed near the town of Hinton in Alberta, Canada. Following the collapse of a tailings dam, up to one billion liters () of wastewater flooded into the nearby Athabasca River in what may be the largest coal slurry spill in Canadian history. The river's waters experienced immediate spikes in arsenic, metals, and carcinogenic polycyclic aromatic hydrocarbons (PAHs). Although the Athabasca was deemed safe for drinking and wildlife by the end of the year, the extent of the environment's recovery remains in doubt.
Spill.
Located about east of Hinton, the Obed Mountain Mine was a thermal coal mine with the capacity to produce about 3.2 million tonnes () of coal per year; 2.6 million tonnes () are proven to exist, and up to 84.7 million more tonnes () were posited. Tailings ponds were constructed to contain water used to wash coal; besides wastewater, the pools also contained fine rock and clay particles, unrecovered coal, and flocculents. Operations were suspended in 2012 because of economic pressures, and around of the mine has been reclaimed.
On October31, 2013, one of the mine's tailings dams failed, and from between 600 million to a billion liters () of slurry poured into the Plante and Apetowun Creeks. The plume of waste products then joined the Athabasca River, travelling downstream for a month before settling in Lake Athabasca near Fort Chipewyan, over away.
Environmental impact.
In the first month after the spill, water quality tests revealed the presence of metals and chemicals such as cadmium, arsenic, manganese, lead, mercury, and PAHs in excess of limits for consumption or life along the first of the Athabasca River. Mercury, for instance, was found to be nine times higher than normal, while PAHs were at levels four times higher than the Canadian standard for potable water. As a result, residents were discouraged from both drinking any of the Athabasca as well as watering any livestock or pets. 
By December 2013, as the plume reached Fort McMurray, government officials reported that water from the Athabasca was once again below safety thresholds for both wildlife and drinking water. Monitoring has continued in the years since, although First Nations representatives have continued to dispute the rigor of the sampling program, its exclusion of data from sediment, and the lack of information made available to the public.
Aftermath.
In October 2015, the Alberta Energy Regulator corporation filed charges against the mine's operators, Sheritt Coal and Coal Valley Resources Inc., on several counts of violations of the Environmental Protection and Enhancement, Water, and Public Lands Acts which could amount to up to a $2.2 million fine. Proceedings began on January20, 2016.
In June 2017, Prairie Mines & Royalty, formerly known as Coal Valley Resources, a subsidiary of Sheritt Coal, was fined a total of $4.5 million Canadian Dollars after the company plead guilty to two violations of federal law under the Fisheries Act and one violation of Alberta's Environmental Protection and Enhancement Act.