More pollutants could flow into the Red River at certain times of the year if the province agrees with a city request to loosen the rules to save millions of dollars on upgrades to the city's largest sewage treatment plant.

Coun. Scott Gillingham told reporters Thursday the city's chief administrative officer has been in talks with the province about loosening the environmental licence for the North End sewage-treatment plant upgrades to allow it to exude wastewater effluent — specifically ammonia — at a rolling average level rather than a hard cap on how much can be released at a given time.

"It would allow us to continue to protect the environment, but also could save the citizens of Winnipeg tens of millions of dollars," the city's finance chair said.

Gillingham said if the province allows the city to emit an average over time, Winnipeg would be off the hook for as much as $30 million in construction and design costs for the upgrade.

'What's the value of the 10th largest lake in the world?'

When asked if this regulation change would mean more pollution flowing into Lake Winnipeg, Gillingham said the city is playing its role to protect Lake Winnipeg.

"The overall impact that the city has on the lake … there are great contributors south of the border, the watershed itself," he said.

"I'm not saying the City of Winnipeg shouldn't do our part. I am saying if there could be a small amendment to the licence, the City of Winnipeg would still be doing our part to protect the lake, but it would save tens of millions for the ratepayers."

Biologist Peter Leavitt with the University of Regina says when it comes to nitrogen such as ammonia, timing and the levels released into the river are integral to its health. He argues the concept of allowing a "rolling average" could be detrimental to the fish population of the Red River and by proxy, Lake Winnipeg.

"The reason that there is a maximum safe level is because levels past that are unsafe," Leavitt told CBC News. "The average doesn't mean anything, it just means there some fraction of the year where you are producing damage to the environment."

Leavitt has extensively studied the effects of nitrogen on lakes and says there is no good time of the year to release larger amounts of ammonia into a system. Ammonia release in summer can stimulate the growth of blue-green algae, while its release in spring harms the good algae that organisms rely on. It is dangerous for fish spawn throughout the year, he said.

"It is an economic argument and you have to ask yourself, 'What's the value of the 10th largest lake in the world?' It is $30 million? Is it $3 billion? It's not my call," he said.

Project in the works since 2003

Upgrades to the North End Water Pollution Control Centre, the largest of Winnipeg's three sewage-treatment plants, were ordered by the province in 2003, but likely won't begin in earnest until after 2019.

The $795-million project — the most expensive capital construction job in the city's history — involves building two new facilities at the North End sewage treatment plant.

One facility will remove phosphorus and nitrogen from the effluent at the North End sewage-treatment plant. Right now, these nutrients wind up in the Red River and are carried north to Lake Winnipeg, where they promote the growth of algae that alters the ecology of the lake.

The other facility will dispose of biosolids — partly treated solid waste — produced by all three of the city's sewage plants.

Reporters were told by Gillingham to direct further questions about the direct cost, environmental impact and reaction by the province to chief administrative officer Doug McNeil.

CBC News was denied an interview with McNeil, with a spokesperson offering the following statement, "We can confirm that discussions between the city and province are continuing."

Province says science will prevail

A spokesperson for Sustainable Development Minister Cathy Cox didn't outright say they would deny the request, but said they will maintain restrictions that are supported by science.

"Limits on ammonia levels must be constantly adjusted because of the potential for immediate harm on aquatic species and precautions related to publicly accessed waterways. If not strictly monitored, ammonia can become a lethal concentration for aquatic life and have harmful effects on our province's fragile water ecosystems," said Kalen Qually in a prepared statement attributed to Cox.

According to the province, the current limits for ammonia are based on maximum daily loads over a 24-hour period. The maximum loads vary depending on the amount of flow in the river, the temperature of the water and the life cycle of the aquatic species of concern.