Cultus Lake: Ours to Protect

Cultus Lake is a special place for many British Columbians. Generations of vacationers remember golden summers at its beaches and picnic spots. 

Set in a temperate rainforest, nestled between the mountains at its back and the great Fraser River floodplain in the north, the lake’s ecosystem is a unique legacy of the last Ice Age. When the ice receded, flora and fauna returned and sometimes evolved in isolated pockets. At least two genetically unique populations live here and nowhere else: the Cultus pygmy sculpin and the Cultus sockeye salmon. 

The area is also home to other rare fauna, including the Pacific giant salamander, the coastal tailed frog and the red-legged frog. Other residents include coyote, cougar, black bear, blacktail deer, beaver and many species of birds.

First Nations tradition has it that Cultus Lake was a spiritually powerful place. It was so popular for spirit quests that eventually its special power was depleted, giving the lake its Chinook name, which can be interpreted as “useless”. Yet today we find that the lake still has the power to amaze and delight us. The more we learn about its ecosystems and its surprising wildlife, the better we can protect it into the future.

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The Cultus sockeye is a genetically unique population of salmon. Sockeye usually spawn in rivers and streams but Cultus sockeye spawn exclusively in the lake. They are also the latest to spawn of all the Fraser River sockeye. Cultus sockeye have a unique adaptation to spawning time: eggs that are spawned later actually develop faster. The fry also behave unlike most other sockeye fry: they school and move into deeper waters immediately after swimming up from the gravel, likely an adaptation to the many predators in Cultus Lake.

Cultus Lake sockeye have been counted and studied since the 1920s, longer than any other in B.C, making this salmon population one of the world’s best-documented.

In 2002 Cultus sockeye were designated by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as “endangered”. 

Non-native aquatic species have devastated some of B.C.’s freshwater ecosystems through habitat degradation and competition, predation and interbreeding with native species. 

Watch this eagle fish on the lake!

CLASS also attempts to mitigate the Small Mouth Bass (SMB) who were illegally introduced in the lake around 2018.  The SMB are voracious predators, and poses a significant threat to two native at risk species: the Cultus Lake pygmy sculpin, and the Cultus Lake sockeye salmon, as well the 19 other lake fish and species like crayfish. Learn more here. You can watch a video produced by the Fraser Valley Invasive Species Society here.  

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The Cultus watershed has become home for many invasive plant species. They include Japanese knotweed, tansy, English ivy, morning glory, giant hogweed, yellow flag iris, broom, and many more. And there may be new ones on the way! Most disturbed soils become weed sites. The Fraser Valley Invasive Plant Council has conducted field trips to highlight the invasive plants at Cultus Lake. Invasive plants cost the ecosystem, landscaping and even infrastructure.
 

Despite their often-attractive appearance, invasive plants are one of the five most significant causes of biodiversity loss and change to ecosystem functions, as reported by the Millennium Ecosystem Assessment. They carry potential negative impacts to the economy, environment, and society; therefore, preventative planning and careful budgeting are required.
 

Aquatic invasive species include Eurasian Watermilfoil, which has colonized the littoral area (shoreline) of Cultus Lake. At the same time yellow flag iris is growing in Sweltzer Creek and needs to be managed. Invasive aquatic plants have long been a concern to residents and park managers. Earlier efforts of mitigation did not reduce the Watermilfoil, and in fact made it worse. Cultivation and even hand-pulling techniques were found to be ineffective, as every fragment would float away and create new colonies. 

Boaters and anglers can help keep them out of Cultus Lake. Eurasian Watermilfoil spreads quickly, degrading fish habitat and impairing boating, swimming and fishing activities. This plant has been identified as a major threat to sockeye in Cultus Lake. CLASS is working hard with agencies such as Fraser Basin Council and DFO to research and develop effective methods to combat Eurasian Watermilfoil.   

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What Is It

Researchers tell us that Cultus Lake is in the early stages of cultural eutrophication, or nutrient enrichment.

Cultural eutrophication occurs in a lake when the normal balance of nutrients such as nitrogen and phosphorus becomes skewed. Excessive levels of nutrients trigger a dense growth of plant life, most frequently algae. While this kind of lush growth is desirable in a garden, such an aquatic plant bloom will block out sunlight, absorb oxygen and begin a chain reaction of changes within the body of water. The process will degrade habitat and reduce the oxygen supply for fish and plants. If left unchecked, the lake could become uninhabitable to most aquatic life.

By looking at lake bottom sediment core samples, researchers found Cultus Lake historically had low levels of nutrients and algae. That, coupled with deep, cold water rich in oxygen, made Cultus Lake one of the most productive rearing grounds for its unique sockeye population.

Annika Putt, Master’s Research, SFU :

"Cultus Lake, British Columbia experiences significant anthropogenic nutrient loadings and eutrophication. If continued unabated, these stresses threaten the persistence of two resident species at risk (coastrange sculpin and Cultus Lake sockeye salmon) and the many ecosystem services provided by the lake."

However, the lake’s chemistry has changed unequivocally since the 1950’s, when human activity began to increase in and around Cultus Lake. In a recent study partially facilitated through CLASS, researchers traced the influx of nitrogen and phosphorus to local agriculture, Cultus Lake septic fields and air-borne deposits. Additionally, tens of thousands of gulls deposit their phosphorus-loaded waste into the water when they roost at the lake after feeding in farm fields and the nearby Bailey Landfill. Watch this drone video of seagulls roosting on the lake.

The process of eutrophication is further propelled by climate change and the ensuing increase in lake water temperatures.

But according to researchers such as Dr. Dan Selbie, a respected limnologist and lead scientist at the DFO Research Lab at Cultus Lake, the early symptoms of eutrophication can be reversed. 

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CLASS volunteers take regular measurements of turbidity (Secchi test), temperature and oxygen in the lake and report those numbers to BC's Ministry of Environment where they are graphed here. You can compare this lake to other BC lakes in the charts.

CLASS has also donated a Water Rangers kit to the local school who has a class of Grade 4/5 students who also monitor the lake health at Sweltzer Creek on various aspects. You can see their results here on the Water Rangers site: https://app.waterrangers.ca/locations/9567

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The goal of CLASS since 2007 is to preserve and protect the health of the lake and its watershed for the sake of the environment and for future generations. To do this we engage science and traditional knowledge to discover the nature of Cultus, to understand the factors that threaten the lake’s well-being, and to mitigate and eliminate those threats. 

We meet monthly to discuss matters of concern and interest. Subscribe to our newsletter to be informed.