2016-2020 Cumulative Impact Assessment under the Great Lakes-St. Lawrence River Basin Sustainable Water Resources Agreement Report

Ontario is taking action to protect the water, ecosystems and species in the Great Lakes-St. Lawrence River Basin (Basin), now and for future generations.

As part of this critical work, the government is seeking public input on what actions Ontario should take, if any, in response to the 2016-2020 cumulative impact assessment on water taking from the Basin.

The cumulative impact assessment is a requirement under the Great Lakes-St. Lawrence River Basin Sustainable Water Resources Agreement (SWRA). It presents an assessment of the cumulative impacts of withdrawals (e.g., taking water through pumping wells), consumptive uses (e.g., water lost and not returned through evaporation or through manufactured products) and diversions (e.g., diverting water within or out of the Basin through canals) on the Basin’s water budget. The Basin water budget is an accounting of water that flows into and out of the Basin. These flows vary from year to year either due to variability in climate or due to human activities.

Great Lakes-St. Lawrence River Basin Sustainable Water Resources Agreement

The Great Lakes-St. Lawrence River Basin Sustainable Water Resources Agreement (SWRA) is an agreement signed in 2005 by Ontario, Québec and the eight Great Lakes States (Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania and Wisconsin), collectively referred to as the Parties, to address concerns about large-scale water diversions and bulk exports from the Great Lakes-St. Lawrence River Basin, growing water use demand and effects of a changing climate on water supply and demand.

In Ontario, commitments set out in the SWRA are implemented primarily through the Ontario Water Resources Act (OWRA) and the Water Taking and Transfer Regulation (Ontario Regulation 387/04).

Cumulative Impact Assessments: Overview

Cumulative impact assessments conducted under the SWRA present a water budget for the Great Lakes Basin and each individual lake watershed within the Basin. The individual lake watersheds include Lake Superior, conjoined Lakes Michigan-Huron, Lake Erie, Lake Ontario and the St. Lawrence River.

These assessments help determine if there are changes in the water budget over time and to what extent these changes may be affected by regional climate factors (such as precipitation and evaporation) or human activities (including consumptive uses, withdrawals and diversions of water within or beyond the Great Lakes Basin). The Parties can use cumulative impact assessments to help decide what actions, if any, should be taken to address any identified changes and trends.

A cumulative impact assessment is required under the SWRA upon the earlier of:

• Every five years;
• Each time 190 million litres of water per day on average in any 90-day period has been lost from the Basin since the last assessment;
• At the request of one or more of the Parties.

2016-2020 Cumulative Impact Assessment: Key Findings

In June 2023, a five-year cumulative impact assessment for the period of 2016-2020 was published by the Great Lakes-St Lawrence River Water Resources Regional Body and Great Lakes-St. Lawrence River Basin Water Resources Council.

While the best available data was used, the assessment report notes that the Basin water budget still has significant uncertainty (e.g., estimates of runoff, evaporation).

In 2020, an interim cumulative impact assessment was conducted following a loss of water from the Basin from 2019 to 2020 that was greater than the threshold amount set out in Article 209 of the SWRA (see Appendix C in the Annual Report of the Great Lakes Regional Water Use Database Representing 2020 Water Use Data). The water use data considered in the 2020 interim assessment was included in the five-year cumulative impact assessment for the total period of 2016-2020.

The key findings in the 2016-2020 assessment regarding the water budget of the Great Lakes-St. Lawrence River Basin were:

• During the reporting period, the water budget was primarily influenced by natural inflows (e.g., runoff, precipitation) and outflows (e.g., water flowing out through the St. Lawrence River, evaporation), rather than by consumptive uses or diversions.
• More water was diverted into the Basin than was lost through diversions out of the Basin or consumptive uses during the reporting period.

The key finding related to climate change impacts was:

• Precipitation and evaporation rates within the Basin are increasing and likely to continue increasing over the coming decades due to climate change impacts. This increase will lead to a wetter and hotter climate in the region, which may cause rapid water level changes without significantly affecting long-term average water levels.

No significant threats to the waters of the Great Lakes-St. Lawrence River Basin were identified in the assessment.

Opportunities for Public Input

The ministry is inviting the public to provide comments on what actions Ontario should take, if any, in response to the 2016-2020 cumulative impact assessment, including if regulations should be made under the OWRA to support Ontario’s implementation of the SWRA and, if so, the content of those regulations.

Regulations that could be made under the OWRA relate to the governance and implementation of Articles 203 (The Decision-Making Standard for Management of Withdrawals and Consumptive Uses), 205 (Proposals Subject to Prior Notice), 209 (Amendments to the Standard and Exception Standard and Periodic Assessment of Cumulative Impacts) and 304 (Water Conservation and Efficiency Program) of the SWRA as well as decisions by a director related to permits to take water.

For full details, see OWRA sections 34.6 (Water transfers: Great Lakes watersheds) and 75 (Regulations, water taking, subsections 34 to 34.11).