Photo: Derek Hatfield from Peterborough, Canada · CC BY 2.0Flood mapping exists for Thunder Bay: 8 on record, latest by Lakehead Region Conservation Authority
Fire seldom reaches Thunder Bay: since 1986, 0.1% of the land within 25 km has burned (0.003% a year). Shaking is less of a worry than in most places, at $0.005 a year per $1,000 of building value ($0.030 typical). Radon is higher than usual: 12% of tested homes in the survey area topped the guideline, against 6.6% for the typical town. Hazard risk gives Thunder Bay a grade of A−; its wildfire band pulls it down.
What stands out about Thunder Bay’s hazards
Four national sources, each read for Thunder Bay: earthquakes, radon, past fires and flood studies.
What Thunder Bay faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Thunder Bay grades A− for hazard risk
For Thunder Bay, Risk will be the average of earthquakes and radon, with wildfire added only if it makes the average worse.
Its place: #446 of 866 in Ontario and #869 of 2,589 Canadian towns.
How sure: The seismic figure is a long-run average from NRCan’s model, not a prediction. Small fires and grass fires are largely missing from the national burned-area record.
Wildfire is rare near Thunder Bay: 0.1% of the land within 25 km burned since 1986, 0% within 5 km
Past fire around Thunder Bay’s homes, from the national burned-area record, with the fuel within 5 km.
Low: the land around Thunder Bay burns at 0.003% a year, where the typical Canadian town sees 0.000%.
Thunder Bay’s homes have had no fire within 5 km since 1986; the closest was 12 km away.
Forest thickens with distance from Thunder Bay: 54% of the land within 5 km, 65% within 25 km.
Shares of land within 5 and 25 km of populated blocks: burned at least once in 1986–2025 (CWFIS burned-area composite), forest fuel and grass (fire behaviour fuel types, 2026, 250 m grid).
Burn rate a year, towns in Ontario · highest of 871
Thunder Bay ranks 50th of the 871 towns in Ontario for burn rate, at 0.003% a year; Sioux Lookout leads with 0.16%.
Each bar: the yearly average share of land within 25 km of a town’s homes that burned, 1986–2025 (CWFIS); the seven highest towns of 2,500 people or more.
Beside 2,610 Canadian towns, Thunder Bay reads low, with 92% of them; only 7.5% rank higher.
Bands of the yearly burn rate: low under 0.05%, moderate under 0.25%, high under 1%, very high 1% or more; towns of 2,500 people or more.
Fire danger and active fires (CWFIS)
Canadian Wildland Fire Information System: National Burned Area Composite 1986–2025 and fire behaviour fuel types (2026), Natural Resources Canada. Measured within 25 km and 5 km of each populated dissemination area; past fire, not a forecast.
Thunder Bay is on the flood map inventory: 8 studies, latest by Lakehead Region Conservation Authority
What Canada’s Flood Map Inventory lists for Thunder Bay: who studied flooding and where to see their maps.
The newest of 8 studies covering Thunder Bay is Lakehead Region Conservation Authority’s, from 2020; open its map to see the zones.
| Study | By | Year | Status |
|---|---|---|---|
| Mosquito Creek | Lakehead Region Conservation Authority | 2020 | final · not public |
| Pennock Creek | Lakehead Region Conservation Authority | 2020 | final · not public |
| Kaministiquia River | Lakehead Region Conservation Authority | 2020 | final · not public |
| McVicar Creek | Lakehead Region Conservation Authority | 2019 | final · not public |
| Neebing River | Lakehead Region Conservation Authority | 2018 | final · not public |
| McIntyre River | Lakehead Region Conservation Authority | 2016 | final · not public |
| Northstar Creek | Lakehead Region Conservation Authority | 2014 | final · not public |
| Current River | Lakehead Region Conservation Authority | 1979 | final · not public |
Towns with a flood study on file
69% of towns in Ontario have a flood study, more than Canada’s 58%; Thunder Bay has one too.
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
Mapping around Thunder Bay began in the 1970s; the 2010s saw the most work (4 of 8 studies), the latest in the 2020s.
Study dates as the NRCan inventory lists them, one count per study touching Thunder Bay.
Listed, not scored: a flood study proves a map exists, not that Thunder Bay floods.
The inventory’s own caution (NRCan): “The Canada Flood Map (CFM) does not include every flood hazard map in Canada and may be incomplete or contain inaccuracies. It should not be relied upon as the official source of flood mapping information. Furthermore, if a map appears to be missing, this does not necessarily mean that the area has never been mapped. For the official version of a map, updated information, or confirmation of applicable regulations, please contact the local authority responsible for flood mapping.”
Natural Resources Canada, Canada Flood Map Inventory; links go to each study’s owner.
Earthquakes cost buildings in Thunder Bay just $0.005 per $1,000 a year
Expected yearly building losses from earthquakes, from Natural Resources Canada’s model.
Shaking costs the typical town $0.030 a year; in Thunder Bay it is only $0.005, 0.2 times as much.
Shaking damage a year per $1,000 of building value
The typical town in Ontario expects $0.043 a year in shaking damage; Thunder Bay expects less, $0.005, and Alexandria the most, $0.21.
NRCan seismic risk model (2022): mean yearly building loss per $1,000 of value; medians of towns of 2,500 people or more.
Nearly every one of Canada’s 2,611 towns (96%) expects more shaking damage than Thunder Bay.
Each column: the share of Canada’s towns of 2,500 people or more in that range of yearly loss per $1,000 (NRCan, 2022).
The model counts damage to Thunder Bay’s buildings and their occupants from shaking only: not liquefaction, landslides, tsunami or fires after a quake.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean).
Radon runs high around Thunder Bay: 12% of tested homes over the guideline
Long-term radon tests in homes across the survey area, against Health Canada’s guideline.
More homes than usual test high around Thunder Bay: 12% against 6.6% for the typical Canadian town. Figures for radon tests are published for the Thunder Bay District Health Unit as a whole, not for Thunder Bay alone.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
More homes top the guideline around Thunder Bay (12%) than in the typical town in Ontario (4%); 0.9% went over 600.
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
One test in ten or more tops the guideline around Thunder Bay, as in 22% of Canada’s 2,611 towns; 4.6% go higher.
Each bar: the share of Canada’s towns of 2,500 people or more whose survey area had that share of tests over 200 Bq/m³.
One home in Thunder Bay can be high while next door is low; a three-month test settles it.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011).
Weather and fire alerts for Thunder Bay
Alerts for Thunder Bay come from Environment and Climate Change Canada and, for emergencies, Alert Ready.
| Alert | What it means |
|---|---|
| Warning | Severe weather is happening or about to: act now. |
| Watch | Conditions favour severe weather: be ready. |
| Advisory | Weather that is less severe but could disrupt the day. |
| Special weather statement | Unusual weather worth knowing about. |
| Special air quality statement | Poor air, often wildfire smoke. |
Evacuation orders for Thunder Bay come from the municipality or the province, while CWFIS maps fire danger every day.
Weather alerts (ECCC) · Alert Ready · Fire danger and active fires (CWFIS)
Hazards in the places around Thunder Bay
Wildfire band, earthquake risk, radon and flood studies for each place nearby.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Thunder Bay | Low | $0.005 | 12% | Yes |
| Fort William 52 1,038 · 9.6 km | Low | $0.004 | 12% | Yes |
| Oliver Paipoonge 6,524 · 16 km | Low | $0.005 | 12% | Yes |
Fort William 52 burns a little more than Thunder Bay, in the same low band (low here).
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Thunder Bay faces
Practical steps for Thunder Bay’s hazards, most pressing first.
- Test for three months in winter.
- Over 200 Bq/m³: fix it.
- Kits are cheap; pros test too.
- Never drive through floodwater.
- Move papers and medicines upstairs.
- Ask whether your street is mapped.
- Clear needles and wood nearby.
- Keep a grab-and-go bag ready.
- In smoke, stay in; filter air.
- Has it had a radon test?
- Check the address on the flood map.
- Are flood and wildfire insured?
What this data can and can’t tell you
- Radon is a survey. The radon share comes from about 14,000 long-term home tests in 2009–2011, pooled for now by the 2007 health region Thunder Bay sits in.
- Flood studies aren’t flood zones. A study’s area can be a whole watershed or province, so being on the inventory says a map exists, not that a home in Thunder Bay floods.
- Wildfire counts one way. The wildfire figure is the share of land within 25 km of Thunder Bay’s homes burned each year from 1986 to 2025, past fire rather than a forecast, and it can only lower Risk.
- Earthquakes are modelled. Shaking damage is modelled from the ground, the buildings and the odds of each quake, and published for whole subdivisions such as Thunder Bay’s.
Questions about flooding and hazards in Thunder Bay
How is Thunder Bay’s Hazard risk Grade worked out?
Thunder Bay’s Hazard risk grade is A−, built on earthquakes and radon with a one-sided wildfire input.
Is Thunder Bay at risk of wildfire?
Some, but Thunder Bay’s low band (0.1% of nearby land burned since 1986, latest 2021) is short of the level that counts.
Is radon a problem in Thunder Bay?
The area’s survey found 12% of 108 tested homes above Health Canada’s guideline, so a three-month test is worth doing in Thunder Bay.
Does Thunder Bay flood?
Thunder Bay’s area has been studied for flooding, and the owner’s map shows which streets lie in a zone; the grade leaves flood out.
How big is the earthquake risk in Thunder Bay?
NRCan’s model expects shaking to cost buildings in Thunder Bay $0.005 a year for every $1,000 of their value, on average over many years.
Seismic risk: Natural Resources Canada. Radon: Health Canada. Wildfire: Canadian Wildland Fire Information System. Flood studies: Natural Resources Canada, Canada Flood Map Inventory. Contains information licensed under the Open Government Licence – Canada.
Sources: NRCan, Canada’s Seismic Risk Model 2022 · Health Canada, Cross-Canada Survey of Radon Concentrations in Homes · CWFIS, National Burned Area Composite and FBP fuel types · NRCan, Canada Flood Map Inventory. Under the Statistics Canada Open Licence.
Adapted from Statistics Canada (Census of Population 2021, population estimates 2025, 2021 census boundaries) under the Statistics Canada Open Licence; this does not constitute an endorsement by Statistics Canada. Neighbourhood names in some cities © OpenStreetMap contributors (ODbL).