The city did not tell the stewardship agency responsible for Cootes Paradise about the extent of a years-long spill that dumped 24-billion litres of watery sewage into the protected marsh.

A confidential report obtained by The Spectator shows city councillors have known since January that enough sewage to fill 10,000 Olympic swimming pools escaped undetected over four years from a sewer overflow tank into Chedoke Creek, which outlets into Cootes Paradise.

City officials did not tell the public about the magnitude of the spill, citing concerns about potential lawsuits and an ongoing investigation by Ontario's Ministry of Environment, Conservation and Parks.

But they also chose not to tell the Royal Botanical Gardens, which manages and leads restoration efforts in the 600-hectare wildlife sanctuary that is also a critical fish nursery for Lake Ontario, a protected migratory bird stopover and a National Historic Site.

"I did not know those details, straight up," said Tys Theijsmeijer, RBG's head of natural areas, when told by The Spectator about the estimated amount of leaked sewage.

"That would certainly explain some very puzzling (water quality) test results we saw over several years ... I guess that 24-billion litres would be a rather large part of the answer to that puzzle."

The prominent marsh advocate said the RBG was informed about the leaking tank when the smelly spill went public in July 2018. But he said both the amount and duration of the sewage spill was news to him.

"It was a huge setback for the marsh," said Theijsmeijer, who is known for championing native replanting efforts and the fight against invasive carp in the sensitive fish nursery.

"Basically, all the oxygen was sucked out of the water, the algae growth was rampant ... and so many plants, like water lilies, were just wiped out."

A rueful Chris McLaughlin, who heads the harbour-rehabilitating Bay Area Restoration Council, said the news also caught him unawares.

But at the same time, he noted the "big number" makes sense given his too-close-for-comfort experience padding the creek in July of 2018. "I remember thinking it smelled like a barnyard," he said.

Theijsmeijer told The Spectator months ago he was eagerly waiting to see the city's consulting report on the spill to help inform efforts to clean up the historically polluted Chedoke Creek.

"We are still waiting to see it. Very patiently," he said Wednesday.

City spokesperson Jasmine Graham called RBG experts "very important partners of the city," but acknowledged spill details have so far been withheld from the agency.

"We understand their concern, however our priority at the moment remains the investigation," she said in an email. "We fully expect that at the conclusion of the investigation process we will have the opportunity to share all relevant information."

Graham said the city is "actively working with the ministry" to meet the requirements of investigators and provincial orders related to the spill. The city did not answer questions about what deadlines or specific requirements it faces as a result of provincial orders.

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But the province told The Spectator on Thursday that it issued a new order to the city just last week — and that the municipality faces a Feb. 14, 2020, deadline to submit an ecological risk assessment and, if needed, a remediation plan for Chedoke Creek.

The confidential city reports obtained by The Spectator suggest remediation via dredging could cost as much as $2 million — although there is no guarantee the city will settle on that solution.

An estimated 5,600 cubic metres — or 560 truckloads — of "organic sediment" is identified for potential removal along the creek in one report.

Theijsmeijer said dredging has pros and cons, particularly the removal of nutrient-overloaded, plant-killing sediment versus the disruption of the wildlife that is still surviving along the creek.

Regardless, he expressed hope the RBG — which owns Cootes Paradise — is consulted on the eventual remedial action. "I think the best solution would be for us all to work together," he said.

McLaughlin agreed. "I'm hoping this is a teachable moment," he said.

"Chedoke Creek is one of the most maligned and abused waterways in Ontario, but we have made some positive headway in recent years.

"To see that undone (in the eyes of the public) would be very disappointing."

mvandongen@thespec.com

905-526-3241 | @Mattatthespec

mvandongen@thespec.com

905-526-3241 | @Mattatthespec