After several weeks of very cold weather, a sudden rise in temperature across Southern Ontario has triggered official warnings about rising water levels. The transition from freezing temperatures to mild conditions is causing heavy snow to melt quickly. When this meltwater combines with forecast rain, it puts pressure on river systems that are still partially frozen. Local agencies are now monitoring several waterways for "ice jams"—masses of broken ice that block the flow of water and cause sudden flooding in nearby areas. While some regions are only seeing higher water flow, others are under formal flood warnings. Residents near rivers and streams are being told to stay away from banks and unstable ice.
Timeline of Current Water Conditions
The following events and regional responses show how the risk has developed over the last several days:
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Late January / Early February: Significant snow builds up during weeks of sub-zero temperatures.
February 14–15: Temperatures begin to rise above freezing, starting the melting process.
February 16 (Monday): Elevated flood risks are reported for the Greater Toronto Area (GTA) and surrounding municipalities.
February 18–19 (Wednesday/Thursday): Rain is forecast to join the snowmelt, increasing the volume of water entering rivers.
Current Status: Specific flood warnings are active for the Grand River area, while Halton and Catfish Creek remain under close watch.
Reported Data and Agency Warnings
| Organization | Region Covered | Warning Level | Primary Concern |
|---|---|---|---|
| Grand River Conservation Authority | Kitchener, Waterloo, Guelph, Brantford | Flood Warning | Rapidly rising water and ice jams |
| Conservation Halton | Oakville, Burlington, Milton | Flood Advisory | Snowpack melt and forecast rain |
| Catfish Creek Authority | South of London | Water Safety Statement | Increased water flow; flooding not yet expected |
| TRCA / GTA Authorities | Toronto, Mississauga, Brampton | Flood Watch | Runoff in urban river systems |
"Ice jams can form quickly and lead to sudden increases in water levels and flooding. Ice-covered waterbodies should always be considered unsafe." — Grand River Conservation Authority Statement
Understanding the Mechanics of Ice Jams
The current risk is not just about the amount of water, but how that water moves. As temperatures rise, the ice on rivers begins to weaken and break into large chunks.
These chunks can get stuck at narrow points in the river, such as bridges or sharp turns.
Once a "jam" forms, it acts like a temporary dam, causing the water behind it to rise and spill over the banks.
The mouth of the Grand River is at a higher risk because Lake Erie is still mostly covered in ice, which prevents river ice from flowing freely into the lake.
Regional Differences in Threat Levels
While the entire southern part of the province is experiencing warmer weather, the danger is not the same in every town.
In the Grand River watershed, the combination of a large drainage area and existing ice has led to a full flood warning until Thursday.
In contrast, the Catfish Creek area reports that while the water is moving faster, they do not expect it to leave the banks yet.
Halton region is focusing on the "snowpack"—the dense layer of snow on the ground. They are watching to see if the ground is too frozen to soak up the rain, which would force all the water directly into local creeks.
The Impact of Forecasted Rainfall
Investigation shows that melting snow alone rarely causes severe flooding in these areas. The primary variable is the rain forecast for mid-week.
If the rain is heavy, it acts as a "trigger" for the existing snowmelt.
Does the timing of the rain on Wednesday mean that local systems will reach their peak capacity at the same time the ice is at its weakest?
Historically, Halton officials note that this specific combination—melting snow plus rain—is the most common cause of significant local flood events.
Analysis of the Situation
Experts from various conservation authorities suggest that the danger comes from "fluctuating water levels." When the water goes up and down quickly, it makes the ice on top very unstable.
Key Insights:
Urban Runoff: In cities like Mississauga and Toronto, large amounts of paved surfaces mean water cannot soak into the ground. It runs quickly into sewers and streams.
Lake Effects: High ice cover on Lake Erie creates a "backlog" effect for rivers trying to drain south.
Soil Saturation: If the ground remains frozen beneath the snow, it cannot absorb moisture, leading to 100% runoff into the river systems.
Conclusion of Findings
The evidence shows a clear increase in water levels across Southern Ontario. The primary cause is a rapid change in temperature following a period of heavy snow.
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Current Findings:
Highest Risk Areas: The Grand River watershed and low-lying areas in the Halton region.
Nature of Threat: Sudden flooding caused by ice blockages (jams) rather than a slow rise in water.
Public Safety: Authorities have marked all ice-covered water as "unsafe" due to erosion from underneath by warmer, faster-moving water.
Next Steps:
Residents should monitor local Conservation Authority websites for changes in warning status.
Avoid walking near riverbanks, as the ground may be unstable and the water is moving with significant force.
Clear debris from private drains and catch basins to allow meltwater to move away from homes.
Primary Sources
Global News: Snow melt raising flood risk in parts of southern Ontario - Context on regional warnings and ice jam definitions.
The Weather Network: Ice jams can form quickly - GRCA warns - Details on Lake Erie ice cover and Grand River risks.
CBC News: Flood advisory issued for Halton - Information on the Sunday-to-Friday advisory period.
The Globe and Mail: Southern Ontario faces rising flood risk - Reporting on temperature shifts and community impact.
Datasurfr: Elevated flood risk forecast in parts of Ontario - Specific list of affected GTA municipalities.
