Cultus Lake — Addressing Cultural Eutrophication
Juvenile salmon and trout species from the DFO Chilliwack River Hatchery swim about in a display at the 2019 Cultus Lake Pikeminnow Derby. – Christina Toth photo
About Cultus Lake
Set at the edge of the Cascade Mountain foothills just south of the central Fraser Valley, the Cultus Lake watershed is home to a diverse range of aquatic and land-based wildlife, including two fish species unique to its lake:
Long prized for its tranquil and natural beauty, Cultus Lake is in the ancestral land of the Ts’elqwxeyeq Tribe, which includes the Soowahlie First Nation, and who are part of the Stó:lō Nation. For millennia, their people have gathered on its shores to share stories, to live, to harvest and to fish. Their cultural imprint echoes in familiar names today – Chilliwack, Sumas, Cultus, Sweltzer, sockeye – and the lake remains a deeply important touchstone to Indigenous communities in the area.
A quiet home for about 1,500 year-round residents, the lake community bustles in the summer as more than two million visitors arrive from around the Lower Mainland and beyond to enjoy recreational activities ranging from hiking, swimming, boating and fishing to camping, golf and waterslides.
The year-round home for about 1,500 residents, the lake community bustles in the summer as more than two million visitors arrive to enjoy recreational activities from hiking, swimming, boating and fishing to camping, golf and waterslides.
Cultus Lake, however, is undergoing a process that threatens its unique aquatic species and its natural assets and ecosystems: cultural eutrophication.
Cultural eutrophication occurs when excess nutrients like nitrogen and phosphorus derived from human activity enter into an ecosystem. Nitrogen and phosphates build up in soils, escape into the air as dust and air pollution, and seep into streams and lakes. In the water, the nutrients accelerate plant growth and blue-green algae, which in turn disrupts the ecosystem balance by reducing food sources and dissolved oxygen needed by fish, and so making the aquatic habitat unliveable for many native species.
Eutrophication can disrupt the natural balance and rhythms of the lake, and that would make it difficult for juvenile salmon and other aquatic species to thrive and survive. For humans, the signs of change include fewer native fish species, more invasive species, cloudy water and in later years, toxic blue-algae blooms.
Currently, the lake’s two endemic fish are already deemed to be at risk:
A Bellwether Lake in the Fraser Valley
Researchers at the Cultus Lake Salmon Research Laboratory (DFO Lakes Research Program) have monitored the eutrophication process in Cultus Lake over the past decade. Cultus is a bellwether lake, suggesting that similar cultural eutrophication changes could be expected in other peri-urban freshwater lakes in the Fraser Valley watershed.
In 2014, Fraser Basin Council obtained funding from the Fraser Salmon & Watersheds Program and Canadian Wildlife Federation – Endangered Species Fund to enable a study on nutrient volumes in Cultus Lake and their sources. See:
These findings were further updated with the DFO Lakes Research Program researchers in 2019. See:
The studies identify the main sources of nitrogen and phosphorus to be:
In 2020, in partnership with the Fraser Valley Watershed Coalition, with the DFO Lakes Research Program, and with funds from the Canada Nature Fund – Aquatic Species at Risk, Fraser Basin Council produced a suite of papers about cultural eutrophication intended to raise awareness with the public and community leaders:
Eutrophication Can Be Reversed with the Right Action
Left unchecked, eutrophication will lead to significant ecosystem degradation. The effects of a changing climate and invasive species in the lake make the need for action even more urgent. The negative impacts could bring far-ranging environmental, cultural, social, and economic losses for Cultus Lake and other Fraser Valley communities.
The good news is that people can reverse eutrophication in Cultus Lake by reducing the levels of nutrients entering the lake.
For example, informed by the eutrophication studies, the Fraser Valley Regional District began plans in 2018 to build a Class A-plus septic wastewater system for Cultus Lake communities with the intention to extract most of nitrogen and phosphorus from the treated effluent before it is released into the ground. The new septic treatment system will go a long way to reduce nutrient volumes entering the lake, and will be a model for other communities facing similar challenges.
Fraser Basin Council continues to work with Cultus Lake stewardship groups and community partners to lead the way in finding sustainable solutions to reduce nutrient input from the various sources, in order to protect this critical freshwater resource and the lake’s exceptional inhabitants.
For information please contact Christina Toth, Assistant Regional Manager, Fraser Valley, at .