Mercury contamination in Grassy Narrows, was the man-made contamination of the Wabigoon River in Ontario, Canada. The contamination was described as "one of the worst cases of environmental poisoning in Canadian history" and is linked to an uncontrolled discharge of between 9,000 kilograms (20,000 lb) and 11,000 kilograms (24,000 lb) of mercury from the Dryden Mill's chloralkali plant in Dryden into the headwaters of the 235 km (146 mi)-long Wabigoon River on Lake Wabigoon in the Kenora District of Northwestern Ontario from 1962 until 1970.