Elk/Beaver Lake supports a variety of native and non-native species of plants and animals that play an important role in the overall health and function of the lake ecosystem. Non-native species have been introduced both intentionally and accidentally. Some non-native species have become invasive, out-competing native species.
A healthy community of aquatic plants is essential to maintaining lake water quality and the health of the lake ecosystem. Aquatic plants provide refuge for small aquatic animals (zooplankton and invertebrates) and produce oxygen important for all animals to survive. Depending on water clarity, aquatic plants can grow in lake sediments as deep as 6 meters below the surface of the water.
Native aquatic plant species at Elk/Beaver Lake include: water shield (Brasenia schreher), coontail (Ceratophyllum demersum), Canada waterweed (Elodea Canadensis), whorled water-milfoil (Myriophyllum verticillatum), yellow water-lily (Nuphar lutea), bulrush (Scirpus lacustris), and broad-leaved cattail (Typha latifolia).
Excessive growth of submerged invasive aquatic plants has become a nuisance in Elk/Beaver Lake, impacting the ecological health of the ecosystem and impacting recreation values. An aquatic plant survey conducted in 2016 found 11 aquatic plant species (compared to 60 species in a previous survey conducted in 1985). Native whorled water-milfoil (Myriophyllum verticillatum) and invasive Eurasian water-milfoil (Myriophyllum spicatum) were the most dominant, accounting for more than 95% of aquatic plants. These plants grow very long strands (1-3 m long) and float just under the lake surface in a thick mat.
The CRD has harvested invasive aquatic plants annually from Elk/Beaver Lake since 1979, with the exception of a few years. A new weed harvester was purchased in 2016. Reports indicate that on average 300-450 tonnes of aquatic weeds are removed from Elk/Beaver Lake each year.
Phytoplankton are a group of photosynthetic microscopic organisms that drift in the surface waters of the lake, in the limnetic zone. Phytoplankton include green and brown algae, diatoms, and cyanobacteria (aka blue-green algae). Phytoplankton abundance is related to how much phosphorus and nitrogen are in the lake, and is the main factor that influences lake water clarity. The green colour and murkiness of the water is typically due to green algae in the lake, although lake clarity can also be influenced by suspended solids (ie, soil particles) in the water.
Cyanobacteria (blue-green algae)
Cyanobacteria, also known as blue-green algae have a competitive advantage in Elk/Beaver Lake. They are considered ‘nitrogen fixers’ meaning they can manufacture their own nitrogen from the atmosphere to support their growth. In phosphorus-rich environments, cyanobacteria can thrive and are largely responsible for the toxic blooms that occur in Elk/Beaver Lake. Blooms occur when phytoplankton abundance increases dramatically due to availability of phosphorus, forming visible scum on the surface of the lake.
Analysis of phytoplankton communities in Elk/Beaver Lake in 2014-2015 indicate that cyanobacteria are the dominate group of species, often comprising more than 50% of all species detected.
Learn more about Environmental Concerns relating to cyanobacteria, and actions to address these concerns, under the Elk/Beaver Lake Initiative.
Zooplankton are microscopic animals that drift in the lake water column, throughout various lake zones. Zooplankton are very important in the food-web as they feed on phytoplankton, and provide a food source for larger consumers, like fish. Zooplankton are highly sensitive to changes in aquatic vegetation and the introduction of invasive fish species. Sampling of the zooplankton community in 2014-2015 indicate that zooplankton abundance and diversity is relatively low. These findings could be the result of poor food quality (phytoplankton dominated by cyanobacteria) and high levels of predation from invasive fish (such as bass, pumpkinseed and yellow perch).
The benthos are the community of organisms that live on and in the bottom sediments of the lake, in the benthic zone. Many benthic organisms are important for providing a food source for fish and birds, and play a critical role in decomposing organic material and cycling of nutrients. In Elk Lake, the benthos community is comprised of bloodworms, midges, glass worms, and aquatic earthworms. Sampling of benthos organisms conducted in 2014-2015 indicated a surprisingly low abundance and diversity expected for a lake with high biological productivity. This is likely related to the long periods of very low oxygen at the sediment-water interface. Low benthic abundance may in turn impact fish communities and may indicate poor ecosystem health.
A healthy, diverse fish population is an integral part of ecosystem health and recreational enjoyment. Fish feed on zooplankton, benthos and aquatic plants. Over-grazing by fish on the zooplankton community may be a key factor leading to overabundance of cyanobacteria community. Invasive fish species also impact native aquatic plant abundance and facilitate the dominance of nuisance aquatic weeds, like Eurasian water-milfoil.
Elk/Beaver Lake is the largest freshwater fishery on Vancouver Island. The Ministry of Forests, Lands, and Natural Resource Operations estimates 15,000-18,000 angler days per year. Elk Lake basin is stocked with approximately 18,000 “catchable” rainbow trout each year. Vancouver Island has a relatively small number of native species of fish, and historical accounts indicate that Elk/Beaver Lake had only three species: cutthroat trout, brown bullhead catfish, and prickly sculpin. The majority of current fish species in Elk/Beaver Lake have been introduced either intentionally for recreational fisheries enhancement (rainbow trout) or illegally (yellow perch, largemouth bass, and common carp).
In 2017, a fish inventory was conducted to characterize the overall fish community in Elk/Beaver Lake. After employing a variety of sampling techniques at multiple sites around the lake, no native fish species were captured or observed. A total of 732 fish were captured, including yellow perch (55%), largemouth bass (12%) and pumpkinseed (11%), followed by smaller numbers of bullhead, carp, smallmouth, and rainbow trout. During this study no fish were captured in depths greater than 12 m in Elk Lake, likely as a result of anoxic conditions (no available oxygen). These findings indicate that the lake contains an abundance of undesirable, introduced fish species and suggests no to very low abundance of native species.
The abundance of non-native fish in Elk/Beaver Lake is detrimental to the health of the overall lake ecosystem because it upsets the food-web, reduces biodiversity and contributes to poor water quality. Yellow perch for example consume native zooplankton and benthic organisms. Largemouth bass are aggressive predators of desirable recreation fish such as rainbow trout. Common carp consume desirable aquatic plants facilitating the growth of nuisance plants. Non-native fish also feed on zooplankton. The foraging behavior of non-native fish also stirs up lake bottom sediments and contribute to nutrient issues in the lake, in a process known as bioturbation, further described under Environmental Concerns.
Elk/Beaver Lake is home to the native, endangered western painted turtle (Chrysemys picta bellii) and the introduced red-eared slider turtle (Trachemys scripta). Turtles are often seen basking on near-shore logs or in transit between land-based nests and the water. Turtles at Elk/Beaver Lake reside primarily in Beaver Ponds and some shallow areas in Elk/Beaver Lake. Turtles should always be observed from a distance and never picked-up or moved.
The two species of turtles are easy to discern if you can get a glimpse of their underbelly. The underside of painted turtles is a striking red and black pattern, whereas sliders are yellow and black.
Western painted turtle
Native western-painted turtles require south-facing wetlands for egg-laying and foraging. On Vancouver Island, these habitats are increasingly rare. Important turtle habitat is threatened by wetland degradation, shoreline development, intensive recreational use, and road mortality. Weed harvesting in Elk/Beaver Lake avoids areas identified as important turtle habitat to the greatest extent possible.
Red-eared slider turtle
Red-eared sliders on Vancouver Island likely began life as someone’s pet. They are native to southeastern United States, Mexico, Central America and Brazil, but have become popular pets that are commonly released into natural areas. Introduced turtles that are illegally released into the wild can carry diseases to native turtles who have no immune defense from tropical diseases. They can also compete with native turtles for food and nesting sites.
Most amphibians found on Vancouver Island and the Gulf Islands depend on wetlands for breeding and surrounding forest and shrub areas for foraging. Significant threats to amphibian habitat include wetland degradation, introduced species (fish & bullfrogs), and poor water quality due to sedimentation and pollution from herbicides, pesticides and fertilizers. Fertilizers, including natural fertilizers like manure, increase the nutrients available in the lake and contribute to the occurrence of blue-green algae blooms. Following blooms, blue-green algae decompose and reduce oxygen availability in the lake, impacting amphibian habitat. Healthy aquatic and terrestrial ecosystems are important for the survival of native amphibians. Wetlands and forested areas in and around Elk/Beaver Lake provide habitat for a number of species, local and introduced.
The northwestern salamander (Ambystoma gracile) is a large, dark brown terrestrial salamander found in moist habitats along the west coast of North America. This secretive salamander shelters under decaying logs or in piles of bark, rodent burrows, or other moist hollows or crevices on the forest floor. The observation of adults and egg masses in 2014 indicate that these salamanders breed in the Beaver Lake ponds.
American bullfrogs (Rana catesbiana) are native to Eastern North America, but have been introduced to southern Vancouver Island. Bullfrogs have been known to occur in our region since at least the 1980s. Multiple introductions have occurred both from the release of adult frogs and from the release of tadpoles – likely caught in the Lower Mainland where they have been known to occur since the 1940s. Bullfrogs are typically dispersed from aquaculture, as fishing bait, and as released former pets. Given the highly mobile and migratory nature of this species, once introduced to an area, it is very difficult to control their movements or contain their populations. Removal of shoreline vegetation, introduced fish, a change in the hydro-period (seasonal wet-dry cycle of a wetland), and conversion of temporary ponds to permanent ponds all favour bullfrog establishment.
The range of the bullfrog continues to expand to new locations due to human aided transport and habitat modification. In the last decade, the spread of the American bullfrog has become a concern because of the potential for it to spread from the Saanich Peninsula, where it is well established, to other parts of Vancouver Island.
Research has shown that the presence of carp and sunfish (family Centrarchidae), which include bass and pumpkin-seed fish at Elk/Beaver Lake promote the proliferation of bullfrogs because they feed on macro-invertibrates, such as dragonfly (family Aeshnidae) larvae, reducing the abundance of adults that would normally feed on tadpoles. Bullfrogs also likely contribute to nutrient loading issues in Elk/Beaver Lake through bioturbation, the stirring of lake sediments. This disturbance to lake sediments causes the release of nutrients into the water column, supporting ideal growing conditions for cyanobacteria (blue-green algae) blooms.
Bullfrog management efforts of the CRD have focused on the highest risk areas with the best likelihood of positive outcomes. CRD Parks prioritizes the exclusion of American bullfrogs from the Sooke Lake watershed (Greater Victoria drinking water supply) and the Sooke Hills Wilderness Regional Park Reserve. Between 2006 and 2013, an estimated 30,000 bullfrogs had been captured and killed, but the population keeps growing. The cost of preventing bullfrog populations from expanding into the Sooke Lake watershed is approximately $74,000 per year. Population control has been attempted at Elk/Beaver Lake, however, the effort was largely unsuccessful because minimal bullfrogs were caught, and the extent of surrounding populations (present in many local lakes) facilitates migration and re-introduction.
Elk/Beaver Lake and the associated creeks are important breeding and wintering habitat for birds, hosting a wide variety of waterfowl and water birds year round. A study conducted in 1992 revealed 32 species of waterfowl at Elk/Beaver Lake. The most abundant species include American coots, gulls (mostly Glaucous-winged), Canada geese, mallards, common mergansers, ring-necked ducks, hooded mergansers and American wigeons. The greatest number of birds observed at one time were over 20,000 birds in January 1993 during a freezing event where other nearby lakes had frozen over.
Breeding species observed over the course of the study included Canada geese, wood ducks, mallards and hooded mergansers. Other common species that occur at Elk/Beaver Lake include provincially listed, green heron (Butorides virescens). Other notable species include bald eagles, great blue herons, pileated woodpeckers and a number of associated forest birds.
During the 1960s and 1970s, large-bodied, non-native sub-species of Canada geese were introduced to the Capital Region, lower mainland, and interior of BC in order to provide sport-hunting and wildlife viewing opportunities. The introduced sub-species of Canada geese do not migrate like native sub-species of geese do. Native geese are present at Elk/Beaver Lake in large flocks during migration in spring and fall only. The introduced non-migratory Canada geese reside at Elk/Beaver Lake all year round, nesting in the spring throughout the region including sites around Elk/Beaver Lake. These geese moult during the summer at which time they are unable to fly. At this time, they seek refuge on the shoreline and in the lake littoral zone at Elk/Beaver Lake.
Christmas bird counts conducted between 1958 and 2010 show a definitive and exponential increase in the geese population of Greater Victoria. Population surveys conducted in 2011-2012 indicated that geese are utilizing Elk/Beaver Lake primarily from June to August, with over 200 individuals documented.
The main concern over geese in Elk/Beaver Lake are the feces on public beaches and the potential for fecal matter to contribute nutrients to the lakes and impact water quality. Early water quality results indicate that birds contribute less than 0.7% of problematic nutrients in Elk/Beaver Lake (Mckean,1992) however this has not been revisited with recent geese populations sizes. From 1991-2012, the CRD conducted nest surveys and egg addling in Elk/Beaver Lake Regional Park. Current goose management practices conducted by CRD Parks include raking feces off the beach, and the employment of a contractor and dog to chase the geese off the shoreline before the park opens to visitors each day in June and July.
Vancouver Island has an abundance of terrestrial mammals that inhabit various land ecosystems. Mammals play an important role in the ecosystem, from grazers to top carnivores, feeding a various levels of the food chain.
Beavers occur throughout British Columbia, including Vancouver Island, and many other coastal islands with fresh water features (ponds, lakes or streams). Beavers have mostly been excluded from Elk/Beaver Lake. When present, beavers have a significant impact on the lake ecosystem by cutting down trees, digging canals and building lodges. This activity significantly changes local habitat by slowing the movement of water and sediments through the lake, and can change the path of streams caused by flooding and shoreline erosion. While beavers have been known to be disruptive to infrastructure or a nuisance to private landowners, they are a natural and important part of freshwater ecosystems. Beavers are important in creation and renewal of wetlands and also regulate water flow downstream, important during both drought and flood seasons.