by Alana Coulombe, Education programs administrator

The frequency and magnitude of blue-green algal blooms continue to rise across Canada and are expected to be further exacerbated by the impacts of climate change and traditional land use practices. The rise in cyanobacterial blooms brings about health, social, economic, and supply problems in the availability of Canada’s freshwater resources (Codd et al., 2017). 

What is blue-green algae?
Blue-green algae, or cyanobacteria, are photosynthetic microscopic bacteria-resembling organisms found in lakes, ponds, rivers, and streams (Government of Ontario, 2022). Although not normally visible in the water, blue-green algae populations can rapidly multiply when favourable conditions, including sunlight, warm temperatures, and the presence of nutrients, are accelerated during midsummer to early fall (Government of Ontario, 2022). Cyanobacteria can accumulate through the growing season and form blooms that spread across the water’s surface due to low loss rates and the ability to concentrate into surface scums (Pick, 2016). Interestingly, fresh blooms often smell like newly mown grass, while older blooms smell like rotting garbage (Government of Ontario, 2022)! Algal blooms thrive in areas with shallow, slow-moving water due to a complex relationship between their physiological adaptations and interactions with the surrounding ecosystem.

Cyanobacterial blooms negatively impact the ecosystem biodiversity, drinking water supply, aesthetic value, and recreational use of the affected waterbody (Codd et al., 2017). Dense blooms disrupt water clarity, appearing bluish-green in the water like green pea soup or turquoise paint, while very dense blooms often form solid-looking clumps (Government of Ontario, 2022). Eventually, these large blooms die and settle to the bottom of the lake where bacteria decompose the cells through a process that consumes oxygen (Ducks Unlimited Canada, 2023). This process can leave very little to no dissolved oxygen, disrupting the natural balance of the aquatic ecosystem and resulting in the death of aquatic organisms like fish (Ducks Unlimited Canada, 2023).

Impacts of blue-green algal blooms
Did you know that research on algal toxins was largely pioneered in Canada by Paul Gorham, head of Plant Physiology at the National Research Council in Ottawa (Pick, 2016)? Concentrated blue-green algae biomass near shorelines pose risks to human and wildlife health. Cyanobacteria can produce toxins, which are then released into the water when the cells die and rupture (Ducks Unlimited Canada, 2023). These toxins can cause neurotoxicity, hepatotoxicity, and dermatotoxicity, affecting the nervous system, liver function, and skin, respectively (Pick, 2016). The exposure routes which can place humans and animals at risk for ingestion of, or contact, with cyanobacteria and cyanotoxins include oral, dermal, and inhalation (Codd et al., 2017). Drinking inadequately treated water or consuming foods like fish or plants exposed to contaminated water may lead to accidental ingestion (Codd et al., 2017). Exposure can also occur through skin contact during recreation, work, or showering, as well as inhalation of sprays, aerosols, or dust from air‐dried cyanobacterial biomass, although these are less understood than that via ingestion (Codd et al., 2017). Scientists can predict cyanobacterial dominance and bloom propensity based on nutrients and temperature at regional scales, but often find it challenging to predict toxicity (Pick, 2016).

Nutrient enrichment of surface waters, specifically by phosphorus and nitrogen, causes eutrophication which drives algal blooms (Codd et al., 2017). Climate change and food web alterations due to the spread of invasive species and overfishing are also significant stressors of aquatic ecosystems contributing to the rise in algal blooms (Pick, 2016). With increasing algal biomass, shifts in algal communities toward bloom-forming cyanobacteria can occur (Pick, 2016). Therefore, controlling algal biomass and managing toxic cyanobacterial dominance requires limiting excess nutrients and eutrophication, invasive species, and other stressors of aquatic ecosystems.

Limiting algal blooms
Numerous case studies have demonstrated that reduced nutrient loading corresponds to declining cyanobacterial biomass in lakes (Pick, 2016). Limiting the nutrients supplied from point and nonpoint sources will thus reduce the risk of blue-green algae growth and protect Canada’s freshwater resources. For instance, avoiding phosphorus-containing cleaning supplies and ensuring proper sewage treatment will reduce the delivery of nutrients via point sources. Nonpoint sources of nutrients enter waterways when surface runoff from excess rainwater or snowmelt dissolves and carries nutrients from the land into nearby water bodies (Ducks Unlimited Canada, 2023). Runoff that collects near urban areas, sewage disposal systems, fertilized lawns, sewage treatment plants, and soil erosion often contains high levels of phosphorus and nitrogen. Clear-cutting natural vegetation, especially along shorelines, leaves a waterbody susceptible to this nutrient-rich runoff. Nature-based solutions involving native vegetation like the Natural Edge Program help limit non-point source pollution by naturally retaining nutrients on the land, leaving fewer nutrients available to enter waterways.

The role of climate change and invasive species
Evidence suggests that climate warming favours cyanobacteria as warmer lake temperatures are known to accelerate blue-green algae growth (Pick, 2016). As the air warms, the atmosphere will also have a greater capacity to hold water leading to more intense rainfalls and increased surface runoff (Ducks Unlimited Canada, 2023). The increased spread of invasive species, like carp and zebra mussels, contributes to the rise in blue-green algal blooms due to changes in the food web structure (Pick, 2016).

Zebra mussels cover the bottom of a lake.

As aggressive bottom feeders, carp rip up the bottom sediments of lakes re-suspending nutrients that may no longer be bioavailable (Ducks Unlimited Canada, 2023). As filter feeders, zebra mussels feed on algae – but not blue-green algae! This provides a competitive advantage for blue-green algae over other species in the lake (Ducks Unlimited Canada, 2023). In fact, previous studies revealed a temporal and spatial relationship between zebra mussels and the return of cyanobacterial blooms, likely due to the change in nutrient recycling (Pick, 2016).

Canada’s freshwater quality is degrading with increasing shoreland developments, the destruction of wetlands, and the removal of natural vegetation within riparian zones. Many inland lakes across Canada are currently developed at or over-capacity and are headed toward increasing rates of blue-green algal blooms and habitat destruction. Increasing demands on freshwater resources for agriculture, industry, recreation, aquaculture, and domestic uses also contribute to growing problems with toxic cyanobacterial populations (Codd et al., 2017). 

How to take action
If a blue-green algal bloom is suspected, report sightings to your local Algae Watch Program, avoid using, drinking, swimming, or bathing in the water, and restrict pet and livestock access to the water. Rehabilitating shorelands to their natural state through the planting of native plant species can improve freshwater resiliency. Vegetated shoreline buffers have a natural capacity to filter sediments and pollutants from surface runoff, provide wildlife habitat, oxygenate water, and moderate temperatures to protect the freshwater that sustains us all!

This blog is part of a series generously funded by the Ottawa Community Foundation, TD Friends of the Environment Foundation, and the Living Cities Canada Fund of Green Communities Canada. The two-year Ottawa Faith Community Capacity Building Program is led by Watersheds Canada and Greening Sacred Spaces.

References
Codd, G. A., Meriluoto, J., & Metcalf, J. S. (2017). Introduction: Cyanobacteria, cyanotoxins, their human impact, and risk management. In J. Meriluoto, L. Spoof, & G. A. Codd (Eds.), Handbook of cyanobacterial monitoring and cyanotoxin analysis (pp. 1–8). John Wiley & Sons, Ltd. https://doi.org/10.1002/9781119068761.ch1
Ducks Unlimited Canada. (2023). Why is blue-green algae a problem and why is it getting worse? [Video]. YouTube. https://youtu.be/QwocQRRaW6c
Government of Ontario. (2022). Blue-green algae. https://www.ontario.ca/page/blue-green-algae
Pick, F. R. (2016). Blooming algae: a Canadian perspective on the rise of toxic cyanobacteria. Canadian Journal of Fisheries and Aquatic Sciences. 73(7): 1149-1158. https://doi.org/10.1139/cjfas-2015-0470