Walkerton E. coli outbreak

The Walkerton E. coli outbreak was the result of a contamination of the drinking water supply of Walkerton, Ontario, Canada with E. coli and Campylobacter jejuni bacteria. The water supply was contaminated as a result of improper water treatment following heavy rainfall in late April and early May 2000, that had drawn bacteria from the manure of nearby cattle used to fertilize crops into the shallow aquifer of a nearby well.

Source: Wikipedia — Walkerton E. coli outbreak (CC BY-SA 4.0)