Lake Ontario: 2020 Water Levels and Resources

High water levels are expected again on Lake Ontario this year.

Lake Ontario water levels depend primarily on three factors:

(1) Inflows from Lake Erie, which are unregulated and account for approximately 85% of inflows into Lake Ontario. Lake Erie water levels are well above record high levels for this time of year, and are projected to continue to be above previous record levels through the spring.

(2) The seasonal runoff from watersheds, like those in Toronto and Region Conservation Authority’s (TRCA) jurisdiction, that drain directly into Lake Ontario.

(3) The outflow from Lake Ontario, which is regulated at the Moses-Saunders Dam by the International Lake Ontario St. Lawrence River Board (ILOSRB) of the International Joint Commission (IJC). Outflows are influenced by the spring peak flow of the Ottawa River, as the ILOSRB is charged with regulating flows to balance both upstream and downstream risks. Control of the outflow, however, does not ensure full control of Lake Ontario levels or river levels downstream.

The ILOSRB is responsible for the regulation of outflows from Lake Ontario, and also for providing forecasts. The most recent IJC forecast indicates that Lake Ontario remains well above average. However, it is on track to peak well below the record highs of 2017 and 2019.

The peak water level is heavily influenced by rainfall over the course of the spring months. TRCA has already been proactively working with municipal partners in preparation for elevated levels this year.

Further to the Premier’s order of closure of all non-essential workplaces in Ontario amid the novel coronavirus pandemic, and the subsequent release of the Ontario Government’s List of Essential Workplaces on April 2, 2020, TRCA is continuing its construction work and services that support health and safety environmental rehabilitation projects in accordance with this directive.

These projects include flood and erosion hazard mitigation work to protect public safety and municipal infrastructure from these hazards.

Lake Ontario Water Levels: Risks and Impacts

Lake Ontario water levels seasonally rise in the spring and early summer, and Great Lakes water levels also fluctuate between multi-year periods of higher average water levels and lower average water levels according to natural processes.

Currently, periods of seasonally high water levels and periods of seasonally low water levels are elevated on all average water levels. Elevated levels can cause flooding, and also erosion, which occurs when water removes natural or manmade materials along the shoreline.

The greater risk occurs when elevated water levels are coupled with wave action from high winds. Impacts can include shortened beaches, inundation of low-lying areas adjacent to the lake, and erosion to trails.

Notifying the Public

Lake Ontario water level forecasts are issued by the ILOSRB, while wave forecasts are produced by both Environment Canada and the Ontario Ministry of Natural Resources and Forestry. As it does for rivers and streams, TRCA issues public flood messages based on local interpretation of these forecasts.

The Lake Ontario Shoreline Hazard Watch and Warning messages are issued when there is a potential for high water levels and waves along the Lake Ontario Shoreline (within TRCA’s jurisdiction) that could lead to flooding and erosion. The shoreline hazard warning can be issued with, or independent of, the riverine flood messages.

For reference, TRCA issues Shoreline Hazard Watches and Warnings based on the following criteria:

(a) Shoreline Hazard Watch at combined water level of above 75.1 m (IGLD 1985) and forecast offshore waves of greater than 2.0m (related to public safety and erosion risks)

(b) Shoreline Hazard Watch for static water level between 75.5m – 75.7m (IGLD 1985)

(c) Shoreline Hazard Warning for static water level of >75.7m (IGLD 1985)

sample of shoreline hazard watch graphic sample of shoreline hazard warning graphic

In addition, TRCA has posted a Special Notice of Caution for the Scarborough Bluffs.

To view Active Flood Forecasting and Warning messages for TRCA’s jurisdiction, including Shoreline Hazard Watches and Warnings for Lake Ontario, visit this page.

To get hourly water level measurements of Lake Ontario at Toronto, view the Department of Fisheries and Ocean gauge.

TRCA uses the 24-hour average water level from this gauge, whereas the ILOSRB reports a daily average from six different gauges across Lake Ontario. The ILOSRB water level forecasts are adjusted weekly and reflect the probability of continued high water levels on Lake Ontario. View the ILOSRB forecasts.

How You Can Stay Safe

  • Exercise caution around Lake Ontario shoreline areas; elevated lake levels and large waves may make these areas dangerous.
  • Avoid areas that are flooded or are experiencing erosion, and keep children and pets away as trails may be unstable.

You can become better prepared for flooding by knowing your risks, having a plan, and putting together an emergency kit.

Visit TRCA’s Flood Preparedness page for more information on how to prepare your home.

Informational Links