To help manage nutrient loads and mitigate the impacts of harmful and nuisance algae in the Great Lakes, the United States and Canada committed, through the 2012 Great Lakes Water Quality Agreement (GLWQA), to review (and revise if appropriate) the binational phosphorus targets for each of the Great Lakes. The United States and Canada have completed a review of Lake Ontario targets and decided not to revise the existing targets at this time. This decision is based on a scientific assessment for Lake Ontario nutrients undertaken in 2020-2022 and subsequent engagement with partners and the public during 2023.
For Lake Ontario, the existing substance objective for Total Phosphorus concentration in open waters is 10 µg/L and the Total Phosphorus load target is 7,000 MT/yr.
While the United States and Canada have agreed to retain the existing phosphorus targets, domestically both countries will continue to implement nutrient management and science programs to better understand and mitigate the impacts of nutrients in both the offshore and nearshore waters of Lake Ontario.
Background
In 2020, the GLWQA Nutrients Annex Subcommittee established the Lake Ontario Objectives and Targets Task Team to conduct a scientific assessment to determine whether the interim binational Total Phosphorus substance objective and load target for Lake Ontario should be revised. The Task Team represented diverse perspectives from a range of fields, including limnology, modelling, food web ecology, fisheries science, and natural resource and watershed management. The Task Team completed its assessment and submitted their recommendation to the Nutrients Annex Subcommittee in September 2022. Public and partner feedback obtained from engagement efforts led by USEPA and ECCC during 2023 concurred with the recommendation not to revise the existing phosphorus objective and target at this time.
The following infographic summarizes the outcomes of the Nutrients Annex’s assessment:
- Assessing Phosphorus Targets for Lake Ontario (PDF 1.86 MB)
The review of Lake Ontario nutrient targets also informed the development of the Binational Priorities for Science and Action in Lake Ontario to be undertaken in 2023-2025 – the first of which his now complete.
- By the end of 2023, complete the review of interim phosphorus load targets for Lake Ontario.
- By 2025, update binational estimates of annual phosphorus loads to Lake Ontario.
- Conduct coordinated monitoring and modeling to improve understanding of phosphorus inputs, fate, and transport in Lake Ontario.
- By the end of 2025, identify locations where management actions may be needed to address nearshore algae issues in Lake Ontario.
In Canada, please direct any questions or comments to glwqa-aqegl@ec.gc.ca.
In the United States, please direct any questions or comments to glwqa@epa.gov.