leveling,

Montreal did dump raw sewage into the St. Lawrence River for a short period of time during the fall of 2015 while their sewage treatment facilities were being repaired. Montreal has been upgrading the system since and, by 2018, will have the largest ozonation treatment facility for wastewater in the world. Some people think that UV light would be just as good as ozone. Cheap Quebec electricity makes ozone treatment attractive.

http://montrealgazette.com/news/local-news/montreals-waste-water-to-be-cleaned-using-ozone-starting-in-2018