The contamination of the Gorge Creek was caused by the dumping of septic tank sewage and a disinfecting chemical into a stormwater drain, according to the Township of Esquimalt.
Lab results from the creek confirmed the presence of fecal coliform and e-coli, and other evidence suggested the presence of a disinfecting chemical.
Municipal staff traced the deliberate dumping upstream to the vicinity of Craigflower Road, but have not pinpointed where the material was produced.
The contamination, which was originally reported on Saturday and believed to be a sewage spill at the time, caused the cancellation of the sixth annual Gorge Swim Fest at the Banfield Park dock on Sunday.
While the Vancouver Island Health Authority believes there is no risk to human health on the Gorge Waterway beaches, the public and their pets are being asked to avoid entering the Gorge Creek until further notice.
Residents who notice anyone putting liquid into a manhole or catch basin is asked to call the engineering and public works department at 250-414-7108.
Staff are continuing to review any leads as they hope to find the person responsible.