 On March 26, 1970, the Ontario provincial government ordered Dryden Chemical Company to cease dumping mercury into the river system, although the order did not place any restrictions on airborne emissions of mercury by the company.It was estimated that over 9,000 kg of mercury had been dumped by the company into the Wabigoon-English river system between 1962 and 1970.The airborne emissions of mercury continued unabated until the company stopped using mercury cells in its chloralkali process in October 1975; the company closed down in 1976.