Flood Outlook for Lake Ontario

Cataraqui Conservation is issuing a Shoreline Conditions Statement today, advising municipalities and the public of rising water levels on Lake Ontario and the upper St. Lawrence River.
The International Lake Ontario – St. Lawrence River Board (ILOSLRB), who manage Lake Ontario outflows and forecasts water levels, reported the following conditions in their press release on May 1, 2026:

• Persistent precipitation this spring has resulted in rising water levels throughout the Great Lakes-St. Lawrence River basin and flood conditions in many tributaries.
• Since March 1, water levels in Lake Ontario have risen from 74.54 metres (244.55 feet) to 75.30 metres (247.05 feet) by April 30, a total increase of 0.76 metres (2.50 feet) in two months
• Strong winds, when coupled with even moderately high water levels, can result in localized flooding of vulnerable areas along the Lake Ontario shoreline as well as downstream along the St. Lawrence River
• Lake Ontario outflow adjustments will continue frequently in accordance with Regulation Plan 2014 which considers both upstream and downstream conditions
• Lake Ontario typically reaches peak water levels in June, after spring precipitation has subsided, and then begins its seasonal decline.
  • If weather conditions are near average, Lake Ontario is forecasted to reach a seasonal peak between 75.40 m (247.38 feet) and 75.50 m (247.70 feet) in May or June.
  • However, higher water levels are possible if weather conditions are wetter than average. Long-term water levels are difficult to predict, much like weather forecasts.
  • Lake Ontario has reached 75.30 m (247.05 feet) or higher in 33 percent of all years since 1960. While higher than average, this water level is not unusual.
• Community members should continue to monitor conditions in their local area.
• Emergency response is typically provided through local municipalities.

Conditions

The Lake Ontario water level measured today at Kingston is currently 75.30 m IGLD85* which is 0.84 m below the 1:100-year flood elevation of 76.14 m IGLD85.

The current level of the St. Lawrence River measured at Brockville is 75.07 m. This is 0.65 m below the 1:100-year flood elevation of 75.72 m IGLD85 in that area along the river.

Current ILOSLRB forecasts for the seasonal peak of between 75.40 m and 75.50 m on Lake Ontario suggest that water levels will remain 0.3 m to 0.5 m below the record highs of 2017 and 2019 (i.e., 75.8 m and 75.9 m respectively).

*International Great Lakes Datum of 1985 (IGLD85)

Risks

While water levels are not expected to reach the record highs experienced in 2017 and 2019 (i.e., 75.8 m and 75.9 m on Lake Ontario at Kingston and 75.6 m on the upper St. Lawrence River at Brockville) water levels above 75.30 m mark a threshold above which the risk of moderate impacts increases, for some properties.

Documentation from past high-water periods indicates that moderate impacts can occur up to an elevation of 75.5 m and may include:

Costal Properties

Impacts to shoreline docks/boathouses and/or inability to access island properties reported at some locations. A few shoreline homes at risk of water at foundation during storms. Not many reports of septic issues. Modifications made to docks for continued use.

Marina and Yacht Clubs

At top of normal operation range for boat ramps or fixed docks at many facilities; modifications may be required for continued use (low cost).

Municipal and Industrial Water Uses
Reduced sewer capacity.

Municipal Assets

Inundation or erosion impacts to some public shoreline assets (generally very local, and requiring some type of response such as fencing, short term repairs, etc.). Parks and trails flooded and eroded, municipal boat ramps flooded.

Generally, major impacts do not occur until static water levels exceed 75.5 m. However, significant localized impacts driven by wave action can start to occur at lower levels.

Widespread flooding is NOT expected at this time. However, if you witness flooding and/or require assistance your first point of contact is the local municipality.

Staff will continue to monitor ILOSLRB forecasts and Surface Water Monitoring Centre (SWMC) Provincial Statements, and update Cataraqui Conservation messaging as needed. This Shoreline Conditions Statement will remain in effect until (or updated before) Friday, June 12, 2026, at 11:59 PM.

For more information from the ILOSLRB:

• Water levels (updated every weekday): https://ijc.org/en/loslrb/watershed/water-levels
• Flows (updated every weekday): https://ijc.org/en/loslrb/watershed/flows
• Lake Ontario forecast (updated on Thursdays): https://ijc.org/en/loslrb/watershed/forecasts
• Lake Ontario outflow changes (updated in real time as flow changes occur): https://ijc.org/en/loslrb/watershed/outflow-changes#flow_table
• Plan 2014 F limit: https://ijc.org/en/loslrb/watershed/faq/4#4-8-2
• Criterion H14 triggers authorizing deviations: https://ijc.org/en/loslrb/watershed/faq/4#4-8-1
• Ottawa River conditions and forecast (updated daily during freshet): https://ottawariver.ca/
  For up-to-date Lake Ontario and upper St. Lawrence River water levels in your area visit the following Government of Canada links:
• (Kingston) https://tides.gc.ca/en/stations/13988/2026-04-29?tz=EDT&unit=m
• (Brockville) https://tides.gc.ca/en/stations/14400/2026-04-29?tz=EDT&unit=m
• Marine Weather forecasts for Eastern Lake Ontario and upper St. Lawrence River:
  • https://weather.gc.ca/marine/forecast_e.html?mapID=11&siteID=08203 (Eastern Lake Ontario)
  • https://weather.gc.ca/marine/forecast_e.html?mapID=11&siteID=07200 (Kingston to Cornwall)
• For further information on current provincial flood messaging visit www.ontario.ca/flooding
• For up-to-date flooding information, please visit our flood forecasting and information page