Flooding

Last updated April 2, 2025

Heavy rains, an overflowing river, water main breaks and sewer backups can cause flooding. How can you prevent damage to your property? What assistance does the city offer? Find out what to do in emergency situations where there is a risk of water infiltration.

Risks

Heavy rain

Climate change is leading to increasingly intense rainfall episodes. Unusually large quantities of water can overload the city’s sewer system, causing overflows onto the street or property. Also, neighbourhoods where water accumulates more easily are more vulnerable. These are are known as flood-prone areas (see the vulnerability map (in French) )

Water main break, sewer backup or water infiltration 

A broken water main, a leak in a water main, and damaged or improperly installed equipment in your home or neighbourhood can also cause sewer backups or water infiltration.

River overflow 

Water levels in the St. Lawrence River, Rivière des Prairies, Lac Saint-Louis and Lac des Deux Montagnes and weather forecasts are monitored when ice blocks a waterway in the winter and when snow melts in the spring – the two riskiest periods of the year 

If an alert is triggered, the status of the situation and the measures taken on the ground are quickly communicated to residents in affected areas: Ahuntsic-Cartierville, L’Île-Bizard-Sainte-Geneviève, Montréal-Nord, Pierrefonds-Roxboro, Pointe-Claire, Rivière-des-Prairies-Pointe-aux-Trembles, Sainte-Anne-de-Bellevue and Senneville. 

Water level changes (in French) are posted in real time on the Ministère de l’Environnement et de Lutte contre les changements climatiques Web site.

Protecting your building: Renovations and subsidies

Several measures can make your property more resistant to flooding. Waterproof garage doors, backwater and check valves, flat roof draining systems and gutter orientation are just a few examples. There are several subsidies available for such measures and renovations.

Emergencies and disaster relief

Has a large amount of water overflowed from a manhole or has its cover has been moved? Let us know. In the event of a sewer backup, if you believe that a broken water main under the street is the cause, please contact us so our teams can investigate. 

If there is a risk of water infiltration in your home or if you need to evacuate quickly, the city will provide assistance. If your home has been flooded, you will find clear instructions for cleaning each room and making sure that your environment is now safe.

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