Abstract Ontario is lucky to have so many lakes and rivers, containing some of the most abundant fresh water in the world. Unwisely, we still pollute much of it. Since the Walkerton water tragedy, Ontario has put significant effort into protecting those limited water resources that provide municipal drinking water (see Chapter 1). Nothing comparable has been done to protect the rest of Ontario’s lakes and rivers, many of which are being seriously harmed by pollution. This pollution is threatening many provincial aquatic ecosystems, impairing Ontarians’ ability to swim and fish, and harming economic activities that rely on clean water. Government laws and policies have reduced many types of water pollution over the last halfcentury. But big, deliberate gaps in these laws are allowing some water pollution problems to persist or worsen, especially when compounded by population growth and climate change. This chapter examines four significant sources of major pollutants that threaten Ontario’s waters, and the province’s failures to regulate them: 1. Raw municipal sewage – a major source of potentially dangerous pathogens like E. coli, that spoil some Ontario beaches (section 2.2); 2. Agricultural runoff – a major source of phosphorus, that contributes to algae blooms (section 2.3); 3. Industrial wastewater – a major source of metals and toxic chemicals, that can harm aquatic animals and potentially humans (section 2.4), and 4. Road salt – a major source of sodium and chlorides, that damage aquatic ecosystems and can render sources of drinking water undrinkable (section 2.5).

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