Canada

This is fairly common in older cities. Combined sanitary and storm sewers were the norm not too long ago, and separating them, especially in a very flat place, isn't easy.

It should be understood that these events are fairly infrequent and only happen when the combined sewer system is overwhelmed by an intense storm. By the nature of these sewers, the discharge is quite diluted if an overflow happens, and it's not someone just opening a valve and letting pure sewage run into the river.

The city has come a very long way in separating the systems since that 1992 letter that is referenced. Installing a new storm sewer can be quite complicated and require some creative engineering with the constraints of existing infrastructure and property, and only limited elevation to work with. For systems not yet separated, there are control weirs and sometimes huge pumping systems to help pump stormwater to decrease the chance of discharge.

It's easy to construe this as deliberate sewage discharge to skirt regulation or save on treatment or something, but it's a very complex issue and the city is doing what they can with the money they have. Perhaps more urgency is needed, but that bill would be put on the residents of Winnipeg. At the moment, the bigger impact on reducing nutrient load is upgrades to the NE Treatment plant, as the article mentions. I'm sure residents would prefer their tax dollars spent on the most effective measures.