Checking the flood records on an Ontario property

A few years ago, CBC Marketplace sent testers out as Ontario homebuyers. Their reporting found no Canada-wide requirement for a seller or agent to tell a buyer a home sits in a flood-prone area, and on two occasions their testers were told a home was not in a floodplain when public data showed otherwise. Ontario’s own independent flood advisor had already recommended, back in 2019, that properties at risk of flooding be publicly identified. No rule yet requires it.

Put those two facts together and the situation is plain: the information exists, and nobody is obliged to hand it to you. Checking is the buyer’s job, and the owner’s, and it is very checkable. This page is about where to look and what the maps actually say when you find them.

Who maps flood hazards in Ontario

Most flood mapping in Ontario belongs to conservation authorities, watershed bodies that regulate development in flood hazard areas. Where one has jurisdiction, it holds the mapping, answers questions about it, and must approve building in the areas it regulates. You can find yours through Conservation Ontario’s authority map, or by asking the municipality.

The first thing to learn about a property is not whether it is in a floodplain. It is whether anyone has mapped one there at all, because the answer is often no:

• Conservation authorities cover the populated south of the province, and not all of it. Large stretches of cottage country, including Muskoka, Haliburton and the Parry Sound district, have no conservation authority at all.
• Where mapping exists, it was drawn when it was drawn. Some of it is decades old, and the federal government keeps an inventory of what flood mapping exists across the country partly because coverage is so uneven.
• A property with no flood mapping is not a property that will not flood. It is a property nobody has drawn the line for. Those are different statements, and mixing them up is exactly the mistake the Marketplace testers were on the receiving end of.

What a floodplain map records

A regulatory flood map is an engineering estimate. Someone modelled a storm the rules define, usually a very large one with a long return period, and drew the line water would be expected to reach. The line records that estimate, on that date, with that model. It does not record what the creek did in 2019, and it does not promise anything about next spring. Separate records track flooding that has actually happened: the federal historical flood events database holds recorded events, and conservation authorities keep their own flood histories.

How to check, step by step

• Find out whether a conservation authority has jurisdiction where the property is. If one does, ask it directly what regulated and mapped areas touch the property. Many publish their regulation mapping online.
• If no authority has jurisdiction, ask the municipality what flood or hazard mapping its zoning relies on, because some flood knowledge lives in zoning schedules even where no authority exists.
• Ask your insurance broker what flood coverage is available at that address before you are committed to it. The Marketplace investigation reported that a meaningful share of Canadian homes may now be effectively uninsurable for overland flood, and coverage is a question only an insurer can answer.

The question that settles it, and who answers it

That is a records question, and the body that holds the records answers it for free or for a small fee. What nobody can honestly answer is “will this property flood”. A map line is not that answer, and neither is its absence.