Cougar Creek Streamkeepers are reminding North Delta residents about the fragility of our urban waterways after a recent fish kill in Lower Cougar Creek.
In an email to members and supporters, the group says an estimated 300 juvenile salmonids — including coho salmon fry and cutthroat trout smolts — were killed on Tuesday, June 11 by an unknown substance that it's believed entered the creek via the Westview Drive storm sewer outfall.
Investigation by both the Streamkeepers and City of Delta staff could not pinpoint the exact source of the spill or the specific toxin responsible.
Deanie Wong, communications and engagement director for the City of Delta, said the city's climate action and environment team was notified of the incident on June 12 and investigated the same day.
City staff took water quality readings upstream and downstream of the outfall, which did not detect anything out of the ordinary, and the water at the time appeared to be clear.
"The person who reported the incident to the city also didn’t see any discolouration of the water at the time," Wong said in an email to the Reporter.
Staff also opened the manhole at the outfall and tested the water with a chlorine strip, but that test came back negative.
Wong said the city has reported the incident to both the province and Fisheries and Oceans Canada, adding live fish have since recolonized the area, including at the mouth of the outfall.
The city has received eight reports of contaminants in Cougar Creek so far this year, from both direct spills into the waterway and storm sewer discharge. Last year it documented 15 incidents, and 19 in 2022. Wong noted that not every reported incident was a pollution event, however — some were determined to be natural occurrences.
Deborah Jones, rain gardens co-ordinator with the Streamkeepers, said the Westview Drive storm sewer outfall has been the source of many fish kills over the years.
"Sometimes the outfall water contains gill-clogging sediments or a milky liquid that suggests maybe latex paint. Or, if we arrive late on the scene, we may see sediments or residues of some sort deposited on the creek bottom. In these cases, we suspect construction or plumbing work, such as pumping out of an excavation or sump without the filtration that City of Delta requires," Jones said in an email to the Reporter.
"In this instance, however, there was no sign of sediments or residues, nor of car-washing soapsuds. We therefore suspect a chemical that would not 'show' — chlorine, for example — that would flow through the system without leaving a trace. Unlucky fish just happened to be in the wrong place at the wrong time."
A map of drainage catchment areas shared by the Streamkeepers shows the contamination could have come any of roughly 390 properties in the Sunshine Hills and Sunshine Village neighbourhoods.
"These non-point-source pollution events that can come from any one of a great many streets or properties are a major challenge for urban streams and their salmon. Public education is essential, since just a single uninformed resident can accidentally cause a fish kill like this one," Jones said.
Types of toxins that might have caused the June 11 fish kill include harsh household cleaning agents used outdoors, pool/hot tub chemicals, substances used to clean or etch concrete and/or aggregate, and driveway sealants.
In the group's email, the Streamkeepers cited a study in Washington state that tested runoff from coal tar-sealed pavement on juvenile salmon and found that, even after seven months, runoff from sealed areas killed 55 percent of juvenile salmon within 96 hours. The group said other studies have found similar results in other species.
Wong said the city has received at least one report of a fish kill in Cougar Creek each year since 2019, several of those due to suspected or verified chemical discharges.
"Others reported during the summer were likely caused by hot weather, which can dry out watercourses and reduce dissolved oxygen levels to lethal concentrations," Wong said.
Jones said the June 11 fish kill was among the worst she's aware of in Cougar Creek, up there with incidents back in October of 2011 and August of 2022.
"Fortunately, there are still thousands of tiny coho fry in the creek, and no doubt many beautiful 10-centimetre cutthroat trout smolts. Those who were upstream of the spill, and others far enough downstream, were not impacted," Jones said. "But unless and until we get all street runoff filtering through landscaping before entering the creek, our precious North Delta salmon runs remain highly vulnerable to human carelessness.
"As one fish expert said, it's a miracle and a testament to salmon resilience that they manage to survive at all in the toxic soup that pours off our pavements and roofs even in the best of circumstances."
In the aftermath of this latest fish kill, the Streamkeepers are asking residents to remember that all storm drains in streets, parking lots and driveways empty directly into local salmon-bearing streams without filtration or treatment.
"Even if you never deliberately pour anything down a storm drain, toxic chemicals such as pesticides can be washed off your property by rain or hosing and head down the gutter to the nearest storm drain," the group said in its email.
They urge pools and hot tubs should only be drained into sanitary sewers, and harsh cleansers should only be used indoors where drains feed into the Annacis Island Wastewater Treatment Plant.
Streamkeepers also recommend minimizing the use of detergents and soaps when washing vehicles, and doing so either at a carwash or on the lawn or other unpaved surface as these can serve to filter the wash water before it reaches local creeks.
For more tips to help protect local fish, visit cougarcreekstreamkeepers.ca/you-can-help/tips-for-home-and-garden.
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