Harmful Algae Blooms
Measures the number of provinces/territories with water-quality monitoring programs with the potential to estimate the number of water bodies impacted by algal blooms


In addition to their impact on environmental health, algal blooms on freshwater lakes and rivers are a concern for the households, businesses and governments that rely on them as sources of water and for recreational and aesthetic enjoyment. Algal blooms can refer to mass growths of either “true” algae or of other micro-organisms that resemble algae but are, in fact, bacteria (the so-called “blue-green algae” made up of cyanobacteria, for example). Excess phosphorus in water - due primarily to fertilizer run-off from farms but also to sewage and urban stormwater run-off – is an important cause of algal blooms. Climate change is another factor, as warmer water increases plant growth. Invasive species are yet another driver. Zebra mussels, for example, clarify water through their filter-feeding, allowing more light into water and promoting plant growth.

Algal blooms are a concern for several reasons. Blue-green algae can produce liver toxins that are harmful and even lethal to humans and animals if ingested. Non-toxic “nuisance” blooms are also a concern. The “true” algae, Cladophora, for example, commonly fouls shorelines of freshwater lakes with dense, rotting mats. These can clog water intakes and impair water and shoreline quality. The degradation of these mats generates foul odours and can give drinking an unpleasant taste. The rotting mats can also harbour disease-causing bacteria.

Algal blooms can have significant economic costs. The costs of algal blooms on Lake Erie alone are estimated to amount to $5.3 billion over 30 years if nothing is done to reduce phosphorus loading to the lake. Little is known about these costs on other water bodies – but they are likely to be large.

Though Lake Erie is arguably one of the best-known Canadian lake impacted by algal blooms, blooms occur in fact on a large and increasing number of freshwater bodies in Canada. This “rise of slime” has been most dramatic in the large, inland lakes found along the edge of the Canadian Shield: Lake Champlain, Lake Ontario, Lake Erie, Lake of the Woods and Lake Winnipeg. Lake Winnipeg has had the dubious distinction of being called “Canada’s sickest lake”. Many smaller lakes are also affected.

In spite of the increasing extent and seriousness of the issue, an estimate of the total number of freshwater bodies affected by algal blooms across the country is not available today. No monitoring is done by the federal government and the approaches taken to monitoring by provincial agencies vary widely (more details available in our landscape scan here). Moreover, current monitoring approaches do not lend themselves to estimation of the total number of water bodies affected or to an understanding of the severity of the blooms in terms of area affected, duration or concentration of algae and/or toxins. No province provides anything today that could be taken as an accurate estimate of the total number of impacted water bodies within its boundaries. Many provinces monitor and report blooms only for provincially managed beaches. Some provinces (and all territories) provide no quantitative information at all. Given this, there is no possibility of estimating the total number of freshwater bodies impacted by HNABs (hazardous and nuisance algal blooms) in Canada based on data available today.

In order to estimate the total number of impacted water bodies, either the federal or provincial/territorial governments would have to establish statistically valid water-quality monitoring programs. Such programs would have to select random and representative samples of water bodies for standardized monitoring over time. The programs would then have to be permanently funded and staffed so monitoring could be carried out as designed. Until such monitoring approaches are implemented, it will not be possible to report on the number of freshwater bodies impacted by algal blooms or the trend over time

As of December, 2019, no province or territory has a water-quality monitoring program with the potential to estimate the number of water bodies impacted by algal blooms (though Ontario’s Broad-scale Monitoring Program comes close).

The full landscape scan on how the different provinces and territories monitor water bodies for HNABs can be found here.

Last updated December 2019

Our Living Waters Network Members leading this conversation:

If you would like to be part of this conversation, email us at [email protected].

Note: The data presented here represents our best research given the time and resources at hand. We acknowledge there may be errors. This shared measurement system belongs to all members of the Our Living Water Network, so if you have any corrections for us, or ideas to share on this measure, please send us an email at [email protected].

Harmful Algae|Measures the number of water bodies with harmful algal blooms across Canada.
Harmful Algae Blooms|Measures the number of provinces/territories with water-quality monitoring programs with the potential to estimate the number of water bodies impacted by algal blooms
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