The quality of the St. Lawrence is rated as intermediate to good for the period from 2012 to 2014: The water quality is good at 52% of the 27 monitoring sites. There was little change in the situation between 2000 and 2014: The percentage of sites with good or satisfactory quality fluctuated at around 81%, while the percentage of sites with poor or very poor quality went from 13% on average between 2000 and 2007 to 8% on average between 2008 and 2014. Upstream from Montréal, the water quality is good, but further downstream, between Varennes and Sorel, it is deteriorating significantly in the navigation channel and the water mass north of it, i.e. the water masses affected by wastewater discharges by the Montréal, Longueuil and Repentigny wastewater treatment plants. This degradation is caused by bacterial contamination from these municipalities that do not disinfect their wastewater prior to discharge into the river. The bacteriological quality improves in Lake Saint-Pierre and becomes satisfactory downstream. The quality of the water mass flowing south of the navigation channel is good or satisfactory all along the river corridor since the navigation channel acts as a barrier preventing the spread of bacteriological contamination. The water quality at all sampling stations in the Québec City region is good or borders on good.