By 2004, it was reported that the Trent was cleaner than it had been in the last 70–80 years, and that episodic incidents of pollution had also reduced considerably since the 1970s. The river remains vulnerable to these pollution events, such as the one that occurred in October 2009 when an accidental release of cyanide from a factory into the sewer system in Stoke-on-Trent, affected the treatment works at Strongford. This resulted in the release of raw sewage and the chemical into the river, killing thousands of fish, and posing a health risk to river users as far south as Burton.