Is a St. Thomas address in a regulated flood area, and whose map says so?

The Kettle Creek Conservation Authority says the population of its watershed is distributed between an urban core in the City of St. Thomas and a rural periphery, and that the creek's steep drop to Lake Erie results in flash flooding and a high degree of erosion. Its Map Your Property tool looks up an address and highlights regulated areas in red and floodplain in blue; the authority calls the map a screening tool, not a statutory map, and asks owners of a property in a regulated area to contact its staff. The Catfish Creek Conservation Authority lists the City of St. Thomas among the municipalities in its watershed jurisdiction and links its own Map Your Property viewer, and both authorities say a property may cross the boundary of two conservation authorities, in which case both are the ones to contact. The City's zoning adds its own rule: section 4.2.11 of By-law 50-88 does not permit an additional residential unit in a flood plain regulated by the conservation authority having jurisdiction.

A permit from the Kettle Creek authority is needed in a regulated area for work such as putting up a building or structure, enlarging one or adding dwelling units to it, and placing or removing fill, and the authority says its permit does not replace building permits or other approvals from municipal offices. 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 Kettle Creek authority and the Catfish Creek authority are to join the Eastern Lake Erie Regional Conservation Authority on 1 February 2027 or a later date set by regulation.

• KCCA: our watershed: the Kettle Creek watershed, its urban core in St. Thomas and its flash flooding
• KCCA: map your property: the authority's screening map of regulated areas and floodplain
• KCCA: do I need a permit: what needs a permit under Ontario Regulation 41/24
• CCCA: board of directors: the municipalities in the Catfish Creek authority's jurisdiction, St. Thomas among them
• CCCA: environmental planning and permits: the authority's regulation limits and property map
• Zoning By-law 50-88: section 4.2.11, no additional units in a regulated flood plain (PDF)
• 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 St. Thomas home the authority's own map 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 St. Thomas address.

What we cover, city by city See the sample report