Traces of human sewage in Grafton Lake

When we recently conducted a comprehensive ‘state of the water’ report on Grafton Lake – the source of drinking water for half of Bowen island’s residents – we were disappointed but not surprised to find traces of cocaine, caffeine and sucralose, among other pollutants (as reported in the Undercurrent June 13 2025). 

We routinely find these pollutants in water samples collected throughout southern BC, as part of Raincoast Conservation Foundation’s Healthy Waters program.

These compounds are not easily broken down in our bodies, and end up in human waste. Therefore they are useful tracers of human waste and are being widely used to assess wastewater impacts downstream of homes, communities, and businesses in Canada. 

This appears to be the case in Grafton Lake, where their detection indicates that wastewater from upstream septic tanks, along with recreational use, is leaking into the drinking water source for many Bowen Island residents. 

We also detected some pesticides, hydrocarbons and PCBs in Grafton Lake water, but at low concentrations and likely due to background pollution from atmospheric deposition.

Health officials may be reassured by the fact that there were no exceedances of Drinking Water Quality Guidelines, indicating that for many pollutants, the levels in Grafton Lake are deemed ‘safe’. The new Cove Bay drinking water treatment plant will address some of the previous concerns about Grafton Lake water quality. However, there are no guidelines available for 140 out of the 141 pharmaceuticals and personal care products measured in our study, or for many of the other pollutants. This suggests that our findings may not (yet) raise a ‘red flag’, but rather they serve as a warning of emerging water quality concerns in Grafton Lake. Human waste should simply not be getting into our drinking water supply. 

Our hope is that this report provides a basis for community action. 

After all, there is nothing more important than water. 

A version of this article was first published in The Bowen Island Undercurrent.

You can help

Raincoast’s in-house scientists, collaborating graduate students, postdoctoral fellows, and professors make us unique among conservation groups. We work with First Nations, academic institutions, government, and other NGOs to build support and inform decisions that protect aquatic and terrestrial ecosystems, and the wildlife that depend on them. We conduct ethically applied, process-oriented, and hypothesis-driven research that has immediate and relevant utility for conservation deliberations and the collective body of scientific knowledge.

We investigate to understand coastal species and processes. We inform by bringing science to decision-makers and communities. We inspire action to protect wildlife and wildlife habitats.