Urban living generates waste that is usually treated to some degree and then discharged into water bodies. Too much waste can pose a risk to aquatic ecosystems and species. Pollutants can remain environmentally damaging even after passing through conventional sewage treatment. Municipal wastewater, including residential, commercial and industrial wastewater, is the major source of contaminants in the marine environment. In southern Canada, where most Canadians live, much of the municipal wastewater is treated by reducing some of the oxygen, suspended solids, phosphorus and sometimes ammonia and nitrogen to reduce the environmental impact on the receiving aquatic ecosystems. The map shows the percentage of the population without access to sewage treatment by ecoregion.