A lake re-emerges: Analysis of contaminants in the Semá:th X̱ó:tsa (Sumas Lake) region following the BC floods of 2021

Executive summary

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 and 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. 

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.

Conclusions

The catastrophic floods of late 2021 in British Columbia wreaked havoc on homes, farms and businesses, flushing manure, fertilizer, fuels, pesticides and other contaminants into fish habitat. The Semá:th X̱ó:tsa area was heavily impacted, with floodwaters temporarily restoring the lake that had existed prior to its deliberate drainage in the early 20^th century.

The lack of pre-flood baseline data prevents us from adequately documenting the impacts of the floods on water quality in the region, but our analysis after the floods revealed several insights (below).

While traumatic and damaging to the affected communities, the catastrophic floods of 2021 nonetheless revealed an unfortunate truth about the waters of the Semá:th X̱ó:tsa area. The floods brought attention to a notable deficiency in environmental monitoring, removed a shroud of ignorance around water quality and exposed the extent of degraded fish habitat in the Fraser Valley.