Photo: Eva K. / Eva K. · CC BY-SA 2.5In St Mawes, 0.8% of homes face high or medium risk from rivers or the sea and 1% from surface water
On the Environment Agency’s maps, which allow for flood defences, “high or medium” means at least a 1 in 100 chance of flooding from rivers or the sea in any year. St Mawes has no Hazard risk Grade.
What stands out about St Mawes’s hazards
From the Environment Agency’s maps and records and the BGS radon atlas, below.
What St Mawes faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Rivers and the sea
Surface water
Past floods
Flood warnings
Radon
Where the water goes in St Mawes
Turn layers on and off. Blue is the risk from rivers and the sea; pink is where heavy rain collects. Both allow for flood defences.
The river and sea risk follows the South Cornwall Coast and the South Cornwall coast. Surface-water risk is spread across the village, in dips, underpasses and along small streams, which is why more homes are exposed to it.
0.8% of St Mawes’s homes are at high or medium risk from rivers or the sea
The Environment Agency’s national map, allowing for defences. None are in the low-risk band.
Share of each UK town’s homes at high or medium risk from rivers and the sea. 35% of UK towns have none; St Mawes has more than 64% of towns.
The Environment Agency’s Risk of Flooding from Rivers and Sea (NaFRA2, June 2026) counts each postcode’s homes by band; the shares weight those postcodes by Census 2021 households. The EA counts include homes built since 2021.
Heavy rain puts about 1.4 times as many St Mawes homes at risk as rivers and the sea do
Surface water is rain that falls faster than drains and the ground can take it. It is mapped separately from rivers and the sea, and it is not in the Hazard risk Grade.
About 0.6% of homes are at high risk of surface-water flooding (a 1 in 30 chance or more each year) and 0.5% at medium risk. A further 5.1% face a low risk from surface water. That is more than 11% of UK towns.
Our estimate: every address in the village (ONS NSUL) read on the Environment Agency’s Risk of Flooding from Surface Water map (NaFRA2, 2025), each postcode’s share weighted by its Census 2021 households. Neither agency publishes a count of homes for surface water, so treat it as a guide; one street can differ from the next.
St Mawes has flooded in 5 recorded years since 1963
Every flood the Environment Agency has mapped inside St Mawes’s built-up area, newest first. The record is fullest for big river floods; small and surface-water floods are often missing.
- 2017February 2017: The sea came inUnder 1 hectare inside today’s built-up area
- 2016April 2016: The sea came inUnder 1 hectare inside today’s built-up area
- 2014February and October 2014: The sea came inUnder 1 hectare inside today’s built-up area
- 2004October 2004: The sea came inUnder 1 hectare inside today’s built-up area
- 1963November 1963: The sea came inUnder 1 hectare inside today’s built-up area
4 of St Mawes’s households today live inside the outline of a recorded flood.
No flood warning or alert is in force for St Mawes · 59 warnings in 20 years
The Environment Agency has 1 flood warning area and 1 alert area reaching into the village; warnings since the service began in 2006.
Of the 59 warnings, 59 were for South Cornwall coast from Lizard Point to Gribbin Head excluding the Tidal Fal Estuary. 2014 had the most warnings (16); 2018 the most alerts (14).
The most recent warning was on 2 February 2026.
Show the 2 warning and alert areas
| Area | Kind | Since 2006 | Now |
|---|---|---|---|
| South Cornwall coast from Lizard Point to Gribbin Head excluding the Tidal Fal Estuary | Warning area | 59 | None |
| South Cornwall coast from Lizard Point to Gribbin Head excluding the Tidal Fal Estuary | Alert area | 103 | None |
Environment Agency Historic Flood Warnings (first issues only, not updates; “flood watch” counted as an alert before 2011) and the real-time flood-monitoring API. Sign up for free warnings on GOV.UK or call Floodline, 0345 988 1188.
Parts of St Mawes are in radon Affected Areas, up to the Over 30% band
Radon is a natural radioactive gas from the ground; long exposure raises the risk of lung cancer. The atlas gives the chance that a home in each 1 km square is above the UK action level (200 Bq/m³).
100% of St Mawes’s built-up area is in a radon Affected Area (1% of homes or more above the action level), and 100% in squares of 5% or more.
The squares are indicative: each takes the highest band found anywhere inside it, so most homes in a coloured square are below it. Only a three-month test in the home gives a real answer.
BGS/UKHSA Indicative Atlas of Radon in Great Britain, version 3. Check an address at UKradon.org.
Flood risk in the places around St Mawes
Share of homes at high or medium and at low risk from rivers and the sea. Tap a town for its page.
| Town | People | High or medium | Low | Hazard |
|---|---|---|---|---|
| St Mawes | 643 | 0.8% | 0% | — |
| Falmouth | 24,066 | 0.8% | 0.3% | C+ |
| Mylor Bridge | 1,534 | 1.4% | 1.2% | C |
| Penryn | 11,194 | 2.2% | 0.9% | C− |
| Carnon Downs and Devoran | 2,129 | 1.1% | 0.8% | C |
| Mawnan Smith | 1,001 | 0% | 0% | A |
| Perranarworthal | 1,305 | 2.3% | 1% | C− |
| Truro | 23,060 | 0.2% | 0.5% | B− |
Perranarworthal, 5.9 miles north-west, has the most homes at risk around St Mawes (2.3% at high or medium). Mawnan Smith has none.
Get ready for what St Mawes faces
Free warnings, what to do in a cloudburst, and what to check before you move.
- Sign up free for Environment Agency flood warnings by text, call or email.
- Floodline: 0345 988 1188, 24 hours.
- St Mawes’s warning areas include South Cornwall coast from Lizard Point to Gribbin Head excluding the Tidal Fal Estuary.
- Surface water rises in minutes, often with no warning issued: stay out of underpasses and dips.
- Keep the gullies and drains outside your home clear of leaves.
- Report a blocked road drain to the council.
- Test over three months, in a living room and a bedroom.
- Above 200 Bq/m³, a small sump and fan usually fixes it.
- New homes in radon areas are built with protection: basic from 3%, full from 10%.
- Check the address on GOV.UK’s long-term flood risk service: it gives rivers and sea and surface water separately.
- Ask whether the home has flooded or had a flood insurance claim; the TA6 property form asks the seller.
- Homes built before 2009 can get flood cover through Flood Re, the government-backed scheme; newer homes can’t.
- Check radon for the address on UKradon.org (a small fee) or ask the seller for a test result.
What this data can and can’t tell you
- Defences are counted. Both agencies’ maps allow for flood defences and the chance they are overtopped or fail, so a town behind a defence scheme can show few homes at high risk and many at low risk.
- Surface water is our estimate. Neither agency publishes a count of homes at risk from surface water, so we read each address on the map. A flat on a hill and a basement in a dip can share a postcode.
- Past floods are what was recorded. The flood outlines come from surveys, aerial photographs and reports; many small floods, and most surface-water floods, were never mapped.
- One town, many streets. Risk is street by street. Check a specific address on GOV.UK’s long-term flood risk service before you buy or rent.
Questions about flooding and hazards in St Mawes
Does St Mawes flood?
The last flood the Environment Agency recorded inside the village was in February 2017. 0.8% of homes are at high or medium risk from rivers and the sea on the Environment Agency’s maps, which allow for flood defences. About 1% of homes are at high or medium risk from surface water, when heavy rain overwhelms the drains.
Which parts of St Mawes are at risk of flooding?
From rivers and the sea, the places the Environment Agency warns directly: South Cornwall coast from Lizard Point to Gribbin Head excluding the Tidal Fal Estuary. Surface water can collect in low spots anywhere in the village. Check a specific address on GOV.UK’s long-term flood risk service.
When did St Mawes last flood?
The recorded flood outlines inside the village run from 1963 to 2017 (5 years); the largest was in 2004. Flood warnings have been issued for parts of the village since 2006, most recently on 2 February 2026.
Is St Mawes at risk of surface water flooding?
About 0.6% of homes are at high risk and 0.5% at medium risk from surface water, against 0.8% at high or medium risk from rivers and the sea. Surface water floods come with little warning, and the agencies don’t issue warnings for them.
Is radon a problem in St Mawes?
100% of the village’s built-up area is in a radon Affected Area on the BGS/UKHSA atlas, and 100% is in 1 km squares where 5% or more of homes may be above the action level. Most homes are below it; a three-month test is the only way to know.
Are there flood warnings in St Mawes now?
No flood warning or alert was in force near St Mawes at 5 November 2026, 06:57. Live warnings are on GOV.UK’s Check for flooding service and Floodline, 0345 988 1188.
Contains Environment Agency information © Environment Agency and/or database right 2026. Contains British Geological Survey materials © UKRI 2026.
Sources: Environment Agency Risk of Flooding from Rivers and Sea, postcodes in areas at risk (June 2026); Natural Resources Wales Flood Risk Assessment Wales (May 2026); ONS Census 2021 households by postcode · Environment Agency Risk of Flooding from Surface Water (NaFRA2, 2025) and Natural Resources Wales Flood Risk Assessment Wales surface water and small watercourses, read at every address (ONS National Statistics UPRN Lookup, September 2026) and weighted by Census 2021 households by postcode · Environment Agency Recorded Flood Outlines and Natural Resources Wales historic flood map, inside the ONS 2022 built-up-area boundary · Environment Agency real-time flood-monitoring API · Environment Agency Historic Flood Warnings (January 2006 to June 2026) and flood warning and alert areas · BGS/UKHSA Indicative Atlas of Radon in Great Britain, version 3, by 1 km square · TownRatings grades: our own summary of the data, ranked against UK towns only. All under the Open Government Licence v3.0.
Contains public sector information licensed under the Open Government Licence v3.0. Contains HM Land Registry data © Crown copyright and database right 2026. Contains OS data © Crown copyright and database right 2026 (ONS boundaries). Northern Ireland: Source: NISRA; contains Land & Property Services data and Ordnance Survey of Northern Ireland information, © Crown copyright, licensed under the Open Government Licence v3.0. Scotland: contains National Records of Scotland data, Registers of Scotland data and SEPA data, © Crown copyright / © SEPA 2025, licensed under the Open Government Licence v3.0.