Assessing whether the 2021 floods caused a spillover of pollutants into fish habitat in the lower Fraser Valley

A Raincoast-led science intervention to inform risk assessment, source identification and recovery in the former Sumas Lake area.

The catastrophic floods caused by a series of atmospheric rivers, early and sudden snowmelt in the mountains, and several dike breaches overwhelmed homes, farms, and industry in parts of southern BC in late 2021. The result was not only floods, destruction, and suffering, but also an uncontrollable soup of ill-described water pollution that threatened drinking water supplies, farm soils and fish habitat.

The extensive habitat needs of salmon in freshwater and marine environments during their anadromous life cycle compels them to navigate a gauntlet of urban, industrial, and agro-forestry activities in watersheds and coastal areas. Pollution and habitat destruction from a century of development have degraded the quality of the water salmon depend on to feed, grow, and reproduce. Rapidly rising flood waters visibly overran industrial sites, farmlands, and wastewater treatment plants, very likely adding to pre-existing water quality challenges for salmon.

A variety of pollutant classes have impacted populations of North American and European salmon and trout in the past, including acid rain, metals, pesticides, dioxins, and hydrocarbons. The degree to which these and/or other contaminants of concern are present in salmon watersheds in British Columbia is not entirely clear, as there has been only limited and sporadic research on the topic. Without data, it is not possible to determine whether the floods exacerbated already degraded fish habitat, so we at Raincoast embarked upon an emergency water sampling program in the Sumas area during a 10-week period between December 2021 and February 2022. We could not do this on our own, and benefited from the participation and financial support of the Lower Fraser Fisheries Alliance (LFFA), the S’ólh Téméxw (STSA), the Pacific Salmon Foundation, BC Environment, and Fisheries and Oceans Canada. 

Drone image of Sumas Prairie farm fields flooded.

Our program was designed and implemented on the fly, as conditions changed daily and planning evolved in conversation with the many organizations and agencies that stepped up. However, our mission was crystal clear: To collect samples of surface water from the waterways of the Sumas Prairie, all theoretically (or more accurately, historically) fish habitat. To underscore the point, the Pacific Salmon Foundation and field technicians from the Semá:th and Leq’á:mel Nations were rescuing live coho salmon from a flooded farm field as we began our work! We collected samples of surface water and submitted these to two analytical laboratories (Caro Analytical Services and SGS AXYS). 

In the absence of pre-flood data on water-borne contaminants in the area, we conducted a wide-ranging approach to laboratory analysis, setting ourselves up for a forensic evaluation that would inform risks to fish habitat and help us to determine the sources of contamination. 

Read our last Notes from the field for some background on our field days getting water quality samples.

What we are looking for

Water Properties

Salmon depend on cold, clean, flowing water in order to complete their life cycle, which begins and ends in freshwater habitat. The two most important parameters for determining whether habitats can be considered healthy are temperature and dissolved oxygen. 

Water temperature is known as the “master factor”, as water temperature affects growth, feeding rates, metabolism, travel time, and other critical features of salmon life cycles. In a world of changing temperatures and watershed habitat alteration, salmon are extraordinarily vulnerable and subject to stress.

Dissolved oxygen is interrelated with temperature. Colder water can hold more dissolved oxygen, which is created by water moving over rocks and other structures in shallow water, and by wind and currents in deeper water. Aquatic plants also produce oxygen during photosynthesis. If dissolved oxygen levels become too low, fish and other aquatic organisms cannot survive. 


We tend to think of nutrients as beneficial, but too many nutrients can create serious problems in aquatic ecosystems. Excess nitrogen for example, coming from domestic, agro, and forestry operations or natural sources, can cause eutrophication by overstimulating the growth of aquatic plants and algae, which in turn, use up dissolved oxygen as they decompose. Phosphorus is another element used in fertilizers to promote plant growth in agricultural practices, and is also known to cause increased growth of algae and aquatic plants that diminish dissolved oxygen levels. Manure storage, transport or application to farmlands can introduce nutrients (as well as bacteria) to fish habitat in the area. The agricultural production throughout the Sumas area delivers valuable food crops to consumers, but may also be delivering harmful levels of nutrients to fish habitat.


Many metals are essential micronutrients to aquatic organisms, however, elevated concentrations can negatively affect their health. Low levels of metals can harm or kill fish by damaging the olfactory and immune systems, and reducing growth rates, swimming performance and reproductive health. In agriculture, copper fertilizers have been used as a fungicide in the management of plant diseases. It is also in the bottom paint of Fraser River boats. Acute, short-term exposure to high levels of copper can cause death, while chronic exposure can affect behaviours such as foraging, predator avoidance, schooling, navigation between fresh and marine water, and reproduction. Chronic, long-term exposure to copper can result in reduced growth and reproductive output. White sturgeon have also been found to be extremely sensitive to copper exposure, particularly in the juvenile life stage. With intensive urban areas and agricultural operations in the Sumas area, it is important to determine whether physical disruption or the intensive use of fertilizers may have released metals into fish habitat.


Pesticides include hundreds of different chemicals designed to kill insects, fungi, or weeds. While the cosmetic use of pesticides has been phased out from many municipal and provincial  jurisdictions in Canada (not including the province of BC), their use in agriculture and forestry in British Columbia is widespread, but their impacts are not clear. The disastrous pesticide DDT was banned in the mid 1970s after catastrophic declines in seabirds, but new generation pesticides that replaced it have been associated with effects on the ability of salmon to find their way to their natal stream, their ability to detect predators and their ability to defend themselves against disease. One remarkable study attributed the loss of millions of Atlantic salmon to the aerial spraying of the pesticide Aminocarb (with an endocrine-disrupting carrier compound) in the fight against spruce budworm in New Brunswick forests. With new-generation pesticides being more water-soluble than their persistent and fat-soluble precursors (such as DDT), there is a need  to determine the extent of pesticide contamination in the streams, ditches and canals in the high density agricultural region of the Sumas prairie – flood or no flood.

Pharmaceuticals and Personal Care Products (PPCPs)

Pharmaceuticals and personal care products are likely not products you would think of detecting in local waterways. They comprise hundreds of products used by people and the animal husbandry sector. Many are endocrine disrupting, do not readily degrade in wastewater treatment systems, and reach our waterways. Many of these compounds of concern are man-made, but some are natural, such as estrogen. The detection of caffeine in Puget Sound highlights the unintended consequences of our addiction to coffee. Anti-bacterial soaps prior to regulations released the persistent and toxic Triclosan into aquatic environments. Widespread feminization of fish downstream of wastewater treatment plants in the U.K. underscores the potential of population-level impacts of estrogenic compounds. The presence of this wide-ranging class of contaminants in Lower Fraser Valley waterways is not clear, but the density of farms and communities suggests that there is good reason to investigate. 

Polycyclic aromatic hydrocarbons (PAHs)

Hydrocarbons represent a family of compounds of natural or geological origin, but this class of contaminants garners heightened concern when we refine products to yield gasoline, diesel or oil, or we generate them upon the combustion of wood. Hydrocarbons are toxic at low concentrations, and have been associated with malformations, liver tumours and skin lesions in exposed fish. While catastrophic oil spills from ships, railcars, and pipelines provide dramatic footage for the media, low level or chronic releases through street runoff, industrial operations, and minor spills can repeatedly  degrade aquatic habitat and affect fish. With diesel slicks observed on flood water surfaces, it is important to determine whether hydrocarbons presented a risk to fish in flood-affected areas.

Forever chemicals: Per- and Polyfluoroalkyl Substances (PFAS)

PFAS are a group of human-made compounds that are used widely and take a long time to break down. These compounds are most commonly found in water repellant clothing, non-stick cookware, food packaging materials, and fire suppression foam. Due to their widespread use, they are found across the globe in soil, water, air, and even in humans. While research is ongoing, scientific studies have found that exposure to certain PFAS products can affect the health of biota. With their extremely persistent properties, it is important to determine whether any PFAS products from any source could be found in the waterways of the Sumas prairie.

People working together to take samples of water in jars.
Photo by Alex Harris / Raincoast Conservation Foundation.

About the authors

Peter Ross is Senior Scientist at Raincoast Conservation Foundation.
Kristen Walters is a Biologist at Raincoast Conservation Foundation. 
Janice Kwo is a Biologist with the Lower Fraser Fisheries Alliance.

Further reading

Ross, P. S., Kennedy, C. J., Shelley, L. K., Tierney, K. B., Patterson, D. A., Fairchild, W. L., & Macdonald, R. W. (2013). The trouble with salmon: relating pollutant exposure to toxic effect in species with transformational life histories and lengthy migrations. Canadian Journal of Fisheries and Aquatic Sciences, 70(8), 1252-1264.

Fairchild, W. L., Swansburg, E. O., Arsenault, J. T., & Brown, S. B. (1999). Does an association between pesticide use and subsequent declines in catch of Atlantic salmon (Salmo salar) represent a case of endocrine disruption?. Environmental Health Perspectives, 107(5), 349-358.

Barlak, Rosie (2004). Water quality assessment and objectives for the Englishman RiverCommunity Watershed [electronic resource] : technical report.

Carter, K., 2005. The Effects of Temperature on Steelhead Trout, Colo Salmon and Chinook Salmon Biology and Function by Life State. California Regional Water Quality Control Board.

Cederholm, C. J., D. H. Johnson, R. E. Bilby, L.G. Dominguez, A. M. Garrett, W. H. Graeber, E. L. Greda, M. D. Kunze, B.G. Marcot, J. F. Palmisano, R. W. Plotnikoff, W. G. Pearcy, C. A. Simenstad, and P. C. Trotter. 2000. Pacific Salmon and Wildlife – Ecological Contexts, Relationships, and Implications for Management. Special Edition Technical Report, Prepared for D. H. Johnson and T. A. O’Neil (Managing directors), Wildlife-Habitat Relationships in Oregon and Wash- ington. Washington Department of Fish and Wildlife, Olympia, Washington.

EPA (2001). Salmonid Behavior and Water Temperature. United States Environmental Protection Agency.

Foran, J. A., Hites, R. A., Carpenter, D. O., Hamilton, M. C., Mathews-Amos, A., & Schwager, S. J. (2004). A survey of metals in tissues of farmed Atlantic and wild Pacific salmon. Environmental toxicology and chemistry, 23(9), 2108–2110.

Gheorghe, S., Stoica, C., Vasile, G. G. , Mihai Nita-Lazar, M., Stanescu, E., & Lucaciu, I. E. (2017). Metals Toxic Effects in Aquatic Ecosystems: Modulators of Water Quality. In (Ed.), Water Quality. IntechOpen.

Hecht, S. A., Baldwin, D. H., Mebane, C. A., Hawkes, T., Gross, S. J., & Scholz, N. L. (2007). An overview of sensory effects on juvenile salmonids exposed to dissolved copper: Applying a benchmark concentration approach to evaluate sublethal neurobehavioral toxicity.

Kaiser, 2018. Copper for crop production.

Lorz, H.W., and Williams, R,H. (1978). Effects of several metals on smolting of coho salmon. Oregon Department of Fish and Wildlife. 

Ministry of Environment (1997). Ambient Water Quality Criteria for Dissolved Oxygen.

McIntyre, J. K., Baldwin, D. H., Beauchamp, D. A., & Scholz, N. L. (2012). Low‐level copper exposures increase visibility and vulnerability of juvenile coho salmon to cutthroat trout predators. Ecological Applications, 22(5), 1460-1471.

Mebane, C.A., & Arthaud, D.L. (2010) Extrapolating Growth Reductions in Fish to Changes in Population Extinction Risks: Copper and Chinook Salmon, Human and Ecological Risk Assessment: An International Journal, 16:5, 1026-1065, DOI: 10.1080/10807039.2010.512243

Packman, G.A. (2006). Selection and use of indicators to measure the habitat status of wild pacific salmon. Pacific Fisheries Resource Conservation Council.

Paerl H. (2017). The cyanobacterial nitrogen fixation paradox in natural waters. F1000Research, 6, 244.

Sainju, U. M., Ghimire, R., & Pradhan, G. P. (2019). Nitrogen fertilization I: Impact on crop, soil, and environment. Nitrogen Fixation.

Video – Heavy Metal Salmon: Sub-lethal toxicity in the Skeena by SkeenaWild.

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Chelsea Greer hanging a wildlife camera.