Is a Sarnia address in a regulated flood area, and whose map says so?

The St. Clair Region Conservation Authority names the City of Sarnia among its seventeen participating municipalities. It says Ontario Regulation 41/24 applies in its area to river and stream valleys with their floodplains and slopes, wetlands and the Lake Huron shoreline, and its online mapping tool shades regulated areas red: open the tool, accept the disclaimer and search the address. The authority says not every regulated area may be mapped, that the regulation applies whether an area is mapped or not, and that the tool does not show the full extent of the regulation, so its staff answer for a given property; for a property for sale it offers a formal property inquiry, for a fee, with a letter and mapping.

The authority's permission is needed before a development activity in a regulated area, and it notes that additional approvals may be required from the municipality. The City's zoning by-law also rules out a secondary dwelling unit in areas classified as Natural Hazards on its zoning maps. A regulated-area result governs permits; it is not a forecast that a home will flood, and a home outside the mapped area can still take water through a basement. Under the Conservation Authorities Act as amended in 2026, the St. Clair Region authority is to join the Western Lake Erie Regional Conservation Authority on 1 February 2027 or a later date set by regulation.

• SCRCA governance: the authority's seventeen participating municipalities
• SCRCA Map Your Property: how to look up a property on the authority's mapping tool
• SCRCA permits: the authority's permits under Ontario Regulation 41/24
• SCRCA property inquiry: a written answer and mapping for a specific property
• Bill 97, Plan to Protect Ontario Act (Budget Measures), 2026: Schedule 3 amends the Conservation Authorities Act; the transition date is 1 February 2027 or a later date set by regulation
• Regional conservation authority boundaries (ERO 025-1257): the Province's decision of 10 March 2026 on which authority joins which of the nine regional authorities
• Ontario Regulation 41/24: Prohibited Activities, Exemptions and Permits, the regulation behind every conservation authority's regulated area

Conservation-authority regulated-area and flood plain checks are not currently included in our reports, so for a Sarnia home the authority's own map tool is the place to look. The full report's water and flooding group does cover past floods seen by satellite, nearby creeks, rivers and ponds, and mapped wetlands for any Sarnia address.

What we cover, city by city See the sample report