Water Quality at Elk/Beaver Lake has been deteriorating since the 1950s and has become a cause for concern as it relates to the health of the ecosystem, the impact to recreational, social and cultural activities and public wellbeing.
Efforts are currently underway to address water quality issues through the Elk/Beaver Lake Initiative
Water quality issues at Elk/Beaver Lake are largely the result of high levels of nutrients in the lake. This occurs through a process known as eutrophication, when a body of water becomes overly enriched in nutrients. At Elk/Beaver Lake watershed, this natural process has been sped up by human-related activities in and around the lake that increase the amount of nutrients that enter the lake. Phosphorus in particular is considered to be the most important factor impacting water quality at Elk/Beaver Lake.
Eutrophic lakes ( lakes with high nutrient levels) are often associated with increased aquatic plant growth, poor water clarity, reduced dissolved oxygen levels, deteriorated aquatic habitat, low biodiversity and frequent cyanobacteria blooms.
Learn more about Nutrients in Lakes, and a Vision for a Healthy Lake.
The source of excessive nutrients in a lake is often a combination of internal and external nutrient loading:
External Nutrient Loading
External nutrient loading is caused by nutrients carried by water, sediments and dust particles from external sources and deposited into the lake. External sources include human activities such as land development, road construction, logging and farming that bring additional nutrients into the lake and alter the movement of nutrients across the landscape. Fertilizers for example are a significant source of nutrients, particularly phosphorus that can be problematic when deposited into lake environments. In Elk/Beaver Lake, it is estimated that between 11-29% of total phosphorus in the lake water is attributed to external nutrient sources (Nordin, 2015; Nurnberg, 2016)
Internal Nutrient Loading
Internal nutrient loading occurs when the nutrients in the bottom sediments of the lake are recycled back into the water column. The nutrients in lake sediments have accumulated over time and are a direct function of the amount of external nutrient deposited into the lake. Nutrients locked in the lake sediments are released into the water column by a variety of mechanisms and environmental conditions. The dominant driver for the release of phosphorus from sediments is low oxygen levels at the sediment-water interface. Under low oxygen conditions, phosphorus is released from the sediment and made available in the water column, known as p-release. Under high oxygen conditions, phosphorus remains bound to the sediment, also known as p-burial. Another important mechanisms that influences internal loading of phosphorus is disturbance to sediments by wildlife (bioturbation) or recreational activities. In Elk/Beaver Lake, it is estimated that between 71-89% of total phosphorus in the lake water is attributed to internal nutrient sources (Nordin, 2015; Nurnberg, 2016).
Water Impoundment (dams)
The construction of dams and other structures that impact flow of water on also contribute to the issue of nutrient loading. Dams slow the movement of water through the lake system and cause nutrients to settle in the lake sediment more readily and increase internal nutrient loading. The approximate 7-year residence time of water and dissolved substances in Elk/Beaver Lake is a significant driver of high nutrient levels and elevated lake productivity.
Cyanobacteria (a.k.a Blue-Green Algae)
Elk/Beaver Lake experiences frequent cyanobacteria (blue-green algae) blooms throughout the year. These native, naturally occurring organisms are responsible for life as we know it on earth, by providing oxygen in our atmosphere. In high abundance, cyanobacteria produce a visible blue-green scum on the surface of the lake that may become toxic. The dominance of cyanobacteria can be directly attributed to the high levels of phosphorus in the lake.
Cyanobacteria are always present in freshwater lakes, but not always in high abundance and not always potentially toxic. Microcystis, Aphanizomenon, and Anabaena are the most common cyanobacteria species in our region that have the potential to produce “cyanotoxins”. Ingesting water with cyanotoxins may cause a range of symptoms, including headaches, abdominal pain, damage to liver and brain tissue in humans, and can lead to liver damage or possibly death in dogs and other small mamals. The CRD issues advisories and warning signs for the public to avoid recreational use of the lake when testing confirms the presence of cyanotoxins in concentrations exceeding guidelines for water contact.
Understanding the cause of cyanobacteria blooms in Elk/Beaver Lake is critical to addressing this issue. In Elk Lake basin, blooms typically occur over the winter months from November to March. Blooms in Beaver Lake have historically occurred from August-September, however in 2018 and 2019, blooms have continued in Beaver Lake throughout winter as well.
In Elk Lake basin, a thermocline forms during the summer separating warm surface waters from cooler deep waters. At the surface, photosynthesis and atmospheric oxygen-exchange occurs and maintains a high level of dissolved oxygen. In deep waters below the thermocline, water becomes very low in oxygen as it is isolated from oxygenated surface waters. Decomposers like bacteria found in benthic habitat in sediments use any available oxygen to breakdown organic materials, further reducing available oxygen. In low oxygen conditions, phosphorus is released (p-release) from sediments into the deep lake waters. As surface waters cool in the fall, the thermocline dissolves and the deep and surface waters mix. This allows the phosphorus in the deep water to become available at surface waters and support rapid growth of cyanobacteria. In Beaver Lake basin, a strong thermocline does not form during the summer. Instead, deep and shallow waters mix readily under windy conditions and nutrients are immediately available to promote cyanobacteria blooms. This allows for cyanobacteria blooms to occur throughout the summer and into the fall.
Following rapid growth of cyanobacteria and aquatic plants during the summer and fall, decomposition of these organic materials further contribute to excessive nutrients in the sediments. This high level of biological activity also reduces dissolved oxygen levels, perpetuating water quality issues in the lake.
Learn more about blue-green algae:
Non-native plants and animals have been introduced to native habitats throughout human history, both intentionally and accidentally. Non-native species that out-compete native species are called Invasive Species, and may reduce biodiversity and upset food-chain dynamics. Once established, many invasive species become ubiquitous and difficult to control or eradicate. Invasive aquatic species impacting water quality at Elk/Beaver Lake include:
More information on the listed invasive species can be found under Plants & Wildlife. Significant invasive terrestrial plants persist in the Elk/Beaver Lake watershed. Learn more about these terrestrial Invasive Species.