Manitoba has given Winnipeg 27 years to seriously reduce the amount of diluted sewage flowing into its rivers.

On Friday, Manitoba Sustainable Development gave the city until 2045 to capture 85 per cent of the diluted sewage that flows into city rivers during an average year.

This would be accomplished by replacing some of the city's combined sewers, which carry both stormwater runoff and raw sewage and overflow an average of 22 times a year.

The city has pegged the cost of replacing enough combined sewers to meet this target at about $1 billion. Eliminating all combined-sewer overflows would cost closer to $4 billion, city wastewater engineers say.

In a letter dated Nov. 24, Tracey Braun, director of the environmental approvals branch within Manitoba Sustainable Development's environmental stewardship division, said the city has until the end of August 2019 to come up with a plan to meet the 85-per-cent-reduction target by 2045.

She also said the city should design this plan with enough flexibility to begin a more aggressive replacement schedule by 2030.

The areas in yellow have combined sewers. The green areas of Winnipeg have separate pipes for stormwater and sewage. (City of Winnipeg)

City council water and waste chair Brian Mayes (St. Vital) said this will require the city to spend more money on combined-sewer replacements because the city was expected to have more time to do the work.

Mayes nonetheless said he agreed with the direction from Sustainable Development Minister Rochelle Squires.

"She's doing what she said she'd do and I think it's the right thing to do," the NDP-affiliated city councillor said of the Progressive Conservative minister.

The city's capital budget calls for Winnipeg to spend $26 million on combined-sewer replacements next year.