animal manure getting into rivers.

It was big news in Canada two years ago when an outbreak of E. Coli in Walkerton, Ontario (caused by manure getting into the water supply, and the officials responsible for water testing failing to detect it), killed 7 people and made most of the town sick. The report on the inquiry has just come out in the past week or so. More information than you'll ever need is at http://cbc.ca/news/indepth/walkerton/