What Cities in Ontario Are Flood-Prone?

Flooding in Ontario is becoming more frequent and severe, especially as extreme weather events occur and infrastructure in some communities struggles to keep up. While flooding can happen almost anywhere, certain cities in Ontario face a higher risk than others. 

This list is based on the Flood Risk Canada map, published by Western University and the Institute for Catastrophic Loss Reduction. This interactive map indicates that these cities (or specific areas within them) are at high or extreme risk of annual flooding over the next 25 years: 

• Wallaceburg 
• Chatham 
• Leamington
• Thamesville
• Brantford
• St. Catherines
• Welland
• Hamilton 
• Angus
• Beeton
• Bradford
• Peterborough
• Campbellford 
• Belleville
• Kingston 
• Cornwall
• Ottawa
• Parry Sound
• Sault St. Marie 
• Thunder Bay 

Key takeaways

Flooding in Ontario is becoming more common due to extreme weather, urban development, and climate change. This guide shows which Ontario cities are the most flood-prone, how to check your home’s flood risk, and how to prepare for a flood.

How to find out if you live in a flood-prone area in Ontario

While the list above of Ontario cities at high or extreme risk of flooding can be a helpful starting point, flood risk can vary depending on your exact location within a city.

Follow these steps to find out whether your home is at low, moderate, high, or extreme risk of flooding: 

• Open the Flood Risk Canada map
• Select “Flood Risk”
• Choose either “Current” or “Future Conditions” to see present or projected risks
• Enter your home address 

Knowing your exact flood risk can help you choose the best tenant, condo, or homeowners insurance and avoid surprises down the road.

What causes flooding in Ontario?

Ontario flooding is typically caused by one of three main factors: extreme weather, urbanization, and climate change. 

Extreme weather 

Ontario often experiences extreme weather events that can quickly lead to flooding. Heavy rainfall is the most common trigger, especially when storms dump more water on the ground than rivers can handle. Rapid snowmelt is another major culprit, such as when spring temperatures rise too fast, and all the snow melts at once. In such cases, local waterways can be overwhelmed. 

According to the Toronto and Region Conservation Authority, “When rain falls, or when snow melts, the water either infiltrates the soil or becomes surface flow (also known as runoff). Surface flow rapidly travels overland and through storm sewers, reaching watercourses and causing water levels within the rivers to rise quickly.” 

Urbanization 

Urban development can worsen flooding, particularly in large cities like Toronto, Ottawa, and Mississauga. Paved surfaces such as roads, sidewalks, and parking lots prevent water from soaking into the ground, forcing excess rainwater into storm drains that can become overwhelmed, leading to street and basement flooding. Add aging infrastructure in the mix, and the problem gets worse. 

In an article for the National Observer, Sarah Buchanan of Toronto Environmental Alliance explained, “The primary contributors to urban flooding include extensive paved surfaces that prevent water absorption into the ground. Nearly a quarter of Toronto’s land area consists of paved streets, with significant off-street parking exacerbating the issue.” 

Climate change

Ontario is experiencing more extreme rainstorms, more frequent freeze-thaw cycles, and warmer winters, which increase runoff and strain drainage systems. 

As the Canadian Climate Institute explains, “Warmer air holds more moisture, leading to heavier rainfall and more intense storms. This, combined with melting snow packs, rising sea levels, and changing weather patterns, has created the conditions for more severe and unpredictable flooding.”

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Worst recorded floods in Ontario

Ontario has experienced several devastating floods over the past century. A few of the worst recorded floods include: 

• Hurricane Hazel in 1954
• Winisk River Flood in 1986
• Southern Ontario Flash Flood in 2013
• Ottawa River Floods in 2017 and 2019 

Hurricane Hazel (1954)

Hurricane Hazel was the deadliest flood in Ontario’s history. On October 15, 1954, more than 200mm of rain fell within just 24 hours, causing the Humber and Don rivers to overflow their banks. Homes and infrastructure were destroyed, leaving 1,868 families homeless and 81 dead. 

Winisk River Flood (1986)

On May 16, 1986, a catastrophic ice break on the Winisk River sent huge chunks of ice downstream, washing away the entire community of Winisk in Northern Ontario. Only two buildings remained after the surge, and this destruction forced residents to relocate 30km inland. 

Southern Ontario Flash Flood (2013)

On July 8, 2013, a sudden, intense rainstorm brought 126mm of rain, making it one of Toronto’s wettest days in history. It caused power outages, stranded commuters, and led to many basement floods. 

Ottawa River Floods (2017 and 2019) 

Historic floods across the Ottawa River brought more than 9,000 cubic meters per second in river overflow, an unprecedented level in the past century. These floods caused widespread states of emergency in Eastern Ontario and Quebec, with thousands of residents evacuated and hundreds of homes destroyed. 

How to prepare for a flood in Ontario

Flooding can happen quickly, and being prepared can make a huge difference in protecting your home and belongings. Informed by guidance from Flood Risk Canada, here are some steps you can take to prepare for a flood.

Steps everyone in Ontario should take to prepare for a flood

No matter where you live, preparing the following can help you stay organized and ready to respond:

• Subscribe to real-time flood alerts through a reliable weather app or your local emergency notification system
• Create a household emergency contact list with numbers for local police, fire, hydro, and municipal emergency departments, and keep a copy in an easy-to-access location
• Assemble a basic emergency kit with drinking water, non-perishable food, essential medications, flashlights, and batteries
• Store important documents, such as passports, birth certificates, and property records, in waterproof containers and save copies digitally
• Keep heirlooms, electronics, and other valuables on upper shelves or a second floor
• Clear gutters, downspouts, and nearby ditches at least twice a year
• Get home insurance with overland water, sewer backup, and above-ground water coverage

Steps for those living in low to moderate-risk flood areas in Ontario

If flooding isn’t common in your area but still possible, these preventative steps can help reduce damage and long-term costs:

• Use landscaping that directs water away from your home
• Choose water-resistant or floodproof materials when renovating
• Relocate utilities and appliances, including electrical panels, furnaces, water heaters, and washers/dryers to a higher floor, if possible
• Install a sump pump to help remove excess water that may collect in your basement
• Add backflow valves to your plumbing system to prevent sewage or contaminated water from entering your home

Steps for those living in high-risk flood areas in Ontario

If flooding is a frequent or serious concern, consider implementing these more robust measures: 

• Keep sandbags or other temporary flood barriers on hand
• Invest in major floodproofing measures, such as permanent fixed barriers or a fully elevated home
• Consider relocating to a safer area if repeated flooding poses ongoing risks to your safety, health, or financial stability