A former lake re-emerges: A backgrounder

We assembled a team to assess water quality in the former Semá:th X̱ó:tsa (Sumas Lake) area of the Fraser Valley over a seven-week period after the floods. This is what we found.

The catastrophic floods of late 2021 in southern British Columbia (Canada) and neighbouring Washington State (USA) destroyed homes, farms, and businesses, with excess water spilling debris, animal carcasses, and diesel fuel into historically productive fish habitat. 

We assembled a team to assess water quality in the former Semá:th X̱ó:tsa (Sumas Lake) area of the Fraser Valley over a seven-week period after the floods. We collected water samples from 11 surface water sites and four groundwater sites for comprehensive contaminant analysis and a subsequent risk-based evaluation. We measured 379 analytes (chemical components and bacteria), including 262 anthropogenic contaminants. We examined excess nutrients, metals, fecal coliform, hydrocarbons, pesticides, pharmaceuticals,personal care products, perfluorinated compounds, sucralose, and tire-related chemicals. 

We detected an average of 87 analytes at each location, of which 20 were anthropogenic chemicals not found in nature. 

We compared our results to the strongest Environmental Quality Guidelines (EQGs) available from Canadian jurisdictions. EGQs are benchmarks used to assess the quality of aquatic environments; they are based on the toxicological risks of specific substances to aquatic life. Only 86 of the analytes we measured (23%) had Environmental Quality Guidelines, meaning that risks to fish for 77% of our analytes are not clear.

There were 59 exceedances of EQGs among our 29 surface water samples during our study, suggesting that fish habitat in the Semá:th X̱ó:tsa region was heavily degraded by multiple contaminants. We identified excessive nutrients, metals, hydrocarbons, and pesticides as being the primary pollutants of concern, underscoring the impacts of domestic and agricultural practices on the fish habitat that permeates the area. 

Citation: Ross, P.S., Walters, K.E., Yunker, M. and B. Lo. 2022. A lake re-emerges: Analysis of contaminants in the Semá:th X̱ó:tsa (Sumas Lake) region following the BC floods of 2021. Raincoast Conservation Foundation. Sidney BC Canada. ISBN 978-1-9993892-6-0 This study was made possible by the contributions of the Lower Fraser Fisheries Alliance, the S’ólh Téméxw Stewardship Alliance, Sumas First Nation, Pacific Salmon Foundation, Fisheries and Oceans Canada, and the British Columbia Ministry of Environment and Climate Change Strategy.

Synthesis and full reports available.

While no EQGs are available to interpret the 177 new and emerging contaminants in our study, the widespread detection of cocaine, painkillers, and pesticides raises fundamental questions about the health of an area that is home to both fish and people.

Our findings paint a disturbing picture of habitat quality for salmon and other fish in this area of the Fraser Valley, and highlight our collective failure to monitor and protect these waters today and for future generations.

Government map from 1913 of Sumas Lake prior to drainage (City of Vancouver Archives).
Government map from 1913 of Semá:th X̱ó:tsa (Sumas Lake) prior to drainage (City of Vancouver Archives).

Figure 2 (from Synthesis report)

Water samples collected (surface)29
Groundwater samples collected (wells)4
Water quality analytes measured379
Anthropogenic chemicals measured263
Average number of chemicals detected at each site21
Analytes with available Environmental Quality Guidelines86
Exceedances of EQ Guidelines in surface water samples59
By the numbers: Summary of the study and its findings.

Figure 3 (from Synthesis report)

Fecal coliform641 x
Pesticides135 x
Pharmaceuticals60 x
Nitrogen (total)43 x
Phosphorus19 x
Hydrocarbons7 x
Metals1.7 x
Sumas water quality compared to upstream reference site.

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