Preventing toxic and nuisance algae
Through the Great Lakes Water Quality Agreement, we are working with the United States, the Province of Ontario and other partners to prevent toxic and nuisance algae blooms that threaten human health and ecosystems in the Great Lakes.
Problem with algae
Algae occur naturally in freshwater and are essential to the aquatic food web and healthy ecosystems. However, too much can create algal blooms which can be harmful to humans and the environment. Nutrients such as phosphorus and nitrogen enter aquatic ecosystems and in high amounts, can cause excess algae.
Lake Erie
The algae problem is most acute in Lake Erie, which receives high loads of phosphorus from many sources including runoff from agricultural lands, urban centres, sewage treatment plants and septic systems. While phosphorus is an essential plant nutrient, when levels are too high it can lead to the development of harmful algal blooms.
In 2016, Canada and the United States adopted new targets to reduce the amount of phosphorus entering Lake Erie. Together, they committed to reduce phosphorus loads to the western and central basins by 40% compared to 2008 levels.
In 2018, Canada and Ontario released the Canada-Ontario Lake Erie Action Plan, which identifies more than 120 actions to be taken by governments, industry, the agricultural sector, land owners and others to reduce phosphorus loads entering the lake from Canadian sources.
In 2024, Canada and Ontario released the Canada-Ontario Lake Erie Action Plan Evaluation and Update Report. The report shares accomplishments made by Canada, Ontario and partners. It also outlines new insights and priorities to guide future actions to reduce phosphorus loads to Lake Erie. A complementary Status of Actions table is also available, providing the status of each action under the plan. This table will be updated on an ongoing basis.
Through a Freshwater Action Plan, we combine science and action to prevent toxic and nuisance algae in Lake Erie by:
- implementing the Canada-Ontario Lake Erie Action Plan, targeting areas contributing the highest loads
- conducting science to improve our understanding of nutrients and their impacts and to report on progress
- funding partner-led projects that have the greatest impact on nutrient reductions and encourage others to adopt best management practices
These actions will help prevent toxic and nuisance algae, keep beaches clean, protect habitat and species, protect drinking water, and encourage tourism, recreation and economic growth.
Lake Ontario
Concerns with algae are different in Lake Ontario, where growth and wash-up of nuisance algae are widespread across the lake and harmful algal blooms are local in nature. Phosphorus loads in Lake Ontario also come from a variety of sources, including a significant contribution from Lake Erie via the Niagara River as well as from major urban centres, especially in the west end of the lake.
Lake Ontario is also experiencing a combination of excess nutrients, like phosphorus, in nearshore areas and nutrient decline in the open waters. Too much phosphorus in the nearshore can cause excessive algae growth, while low levels offshore can affect the food web.
Taking action to reduce the threat of toxic and nuisance algae in Lake Ontario will support protecting the health of the Lake Ontario ecosystem, the drinking water for a quarter of all Canadians, continued recreational opportunities for people and communities, and economic growth of the region.
Through a Freshwater Action Plan, we continue to conduct science and assessments to guide targeted action to reduce the occurrence of toxic and nuisance algae in Lake Ontario.
To help manage nutrient loads and mitigate the impacts of harmful and nuisance algae in Lake Ontario, the United States and Canada committed, through the 2012 Great Lakes Water Quality Agreement, to review (and revise if appropriate) the binational phosphorus targets for Lake Ontario.
In 2024, Canada and the United States agreed to retain the existing binational phosphorus targets after completing the review and scientific assessment for Lake Ontario nutrients in 2020-2022 and subsequent engagement with partners and the public during 2023.
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