Thousands of dead fish showed up in the upper section of the Hope Slough in Rosedale.
First Nations leaders, techs and biologists say it was a "toxic spill" that killed juvenile salmon and other species in the slough on the Schelowat reserve, at the end of Annis Road.
They just have to determine the exact cause and source of the oily sheen floating on the water.
The water testing has been ongoing as part of the restoration project, Shxwlistexw te Sqwá:la Shxweli: 'Care for the Life Spirit of the Hope Slough' — a collaborative project between Sqwá, Shwhá:y and Xwchíyò:m First Nations, funded by Fisheries and Oceans Canada (DFO).
It's one of several initiatives the nations are working together on to protect water as a sacred resource, and it's how they came upon the pollution.
Oxygen levels were so low in the slough that many in from that section of the slough system including endangered Salish sucker, trout, and juvenile coho.
Cheam chief Darwin Douglas said in a release: "Water is our most sacred resource. All life depends on it.
Protecting "sacred" water resources like the incredibly biodiverse Sqwá:la (slough) is key, and wherever possible work to restore the health of our waterways.
"Indigenous people have Inherent title and rights to water within our territories, and more importantly, we have an inherent responsibility to protect water."
The Hope Slough has special meaning to local Stó:lō communities with ancient village sites along the system, having sustained First Nations people for thousands of years, Douglas said.
Cheam staff Roxanna Kooistra, Sqwá councillor Eddie Gardner and Lands manager Anna-lise Cooke discovered the "devastating and heartbreaking" fish kill on Sept. 23, during a regular visit to the slough to conduct routine water sampling.
They jumped into action overnight to identify the source of the contamination, by activating an emergency response to contain the toxic spill.
The source is still to be determined but may be related to agriculture and farming activities in the Hope Slough area, officials say.
"We believe that the dumped toxic waste caused a sudden drop in oxygen spanning several kilometres," said Douglas.
Sqwá Councillor Eddie Garder said they've been working hard to protect wild salmon and this is a setback.
"This has to stop! We can no longer tolerate our wild salmon and waterways being killed. We will not stop our efforts to protect our land and waters, we are disappointed at provincial government agencies for continuing to let this devastation take place.
"Enough is enough."
The City of Chilliwack posted signs at the Hope Slough 'Blueway' access points along the slough between Old Yale Road and McGrath Road.
"Staff are in communication with the Provincial and Federal agencies who are the lead agencies for spill investigation and enforcement; as well as Cheam and Skwah First Nations who discovered the issue while working at a habitat restoration site at the slough," city officials said in a water advisory Sept. 25.
Residents are being advised to avoid contact with the slough water as a precaution while sampling results are pending.
