Photo: Neil Theasby · CC BY-SA 2.0In Boston, heavy rain puts more homes at risk than rivers or the sea: 4.5%, against under 0.1%
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. For hazard risk, Boston grades B: #13 of 61 in Lincolnshire.
What stands out about Boston’s hazards
From the Environment Agency’s maps and records and the BGS radon atlas, below.
What Boston 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
Boston grades B for hazard risk
Flood risk from rivers and the sea, against all UK towns.
The share of homes at high or medium risk from rivers and the sea, ranked against every UK town of 1,000 or more: fewer homes at risk is better. Towns with none at high or medium risk are ordered by their share at low risk, so they don’t all share one score. Surface water and radon aren’t graded: they are described below.
Where the water goes in Boston
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 The Wash, the River Witham and the River Welland. Surface-water risk is spread across the town, in dips, underpasses and along small streams, which is why more homes are exposed to it.
Under 0.1% of Boston’s homes are at high or medium risk from rivers or the sea
The Environment Agency’s national map, allowing for defences. A further 100% are at low risk.
Share of each UK town’s homes at high or medium risk from rivers and the sea. 35% of UK towns have none; Boston has more than 36% of towns.
| # | Town | People | High or med. | |
|---|---|---|---|---|
| 1 | Smethwick West Midlands | 56,343 | 0% | |
| 2 | Bootle Merseyside | 53,722 | 0% | |
| 3 | Bloxwich West Midlands | 51,891 | 0% | |
| … | ||||
| 21 | Kirkby Merseyside | 45,559 | under 0.1% | |
| 22 | Brierley Hill West Midlands | 32,311 | under 0.1% | |
| 23 | Boston Lincolnshire | 45,347 | under 0.1% | |
| 24 | Chippenham Wiltshire | 36,084 | under 0.1% | |
| 25 | Farnborough Hampshire | 60,665 | under 0.1% | |
| … | ||||
| 159 | Exmouth Devon | 35,502 | 9.8% | |
| 160 | Caversham Berkshire | 33,038 | 13% | |
UK towns of 32,000 to 63,000 people.
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.
4.5% of Boston’s homes are at high or medium risk from surface water
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 1.3% of homes are at high risk of surface-water flooding (a 1 in 30 chance or more each year) and 3.2% at medium risk: roughly 860 households. A further 11% face a low risk from surface water. That is more than 62% of UK towns.
Our estimate: every address in the town (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.
Boston has flooded in 3 recorded years since 1978, most of all in 2013
Every flood the Environment Agency has mapped inside Boston’s built-up area, newest first. The record is fullest for big river floods; small and surface-water floods are often missing.
- 2025January 2025: River flooding recorded1 hectare inside today’s built-up area
- 2013December 2013: The sea came in101 hectares inside today’s built-up area
- 1978January 1978: The sea came in26 hectares inside today’s built-up area
Floodwater covered 101 hectares of what is now Boston in 2013, the largest flood the record holds here (December).
1,906 of Boston’s households today live inside the outline of a recorded flood.
Since 2013, the largest recorded flood inside the town covered 1 hectare.
No flood warning or alert is in force for Boston · 20 warnings in 20 years
The Environment Agency has 10 flood warning areas and 5 alert areas reaching into the town; warnings since the service began in 2006.
The warning area covering the most of Boston, Area at risk of river and tidal flooding in West Boston, has not had a flood warning since 2006. Of the 20 warnings, 7 were for Waterside properties between Town Bridge and Haven Bridge in Boston and 4 for Wider waterside properties between Grand Sluice and the Docks in Boston.
2013 had the most warnings (12); 2007 the most alerts (10). The most recent warning was on 6 January 2025.
Show the 15 warning and alert areas
| Area | Kind | Since 2006 | Now |
|---|---|---|---|
| Waterside properties between Town Bridge and Haven Bridge in Boston | Warning area | 7 | None |
| Wider waterside properties between Grand Sluice and the Docks in Boston | Warning area | 4 | None |
| Tidal flooding in the South of Boston and surrounding areas | Warning area | 3 | None |
| Tidal flooding in the East of Boston and surrounding areas | Warning area | 3 | None |
| Isolated properties and villages in the east of the South Forty Foot Drain | Warning area | 3 | None |
| Tidal flooding in areas to the North of Boston, including Frithville and Boston Long Hedges | Warning area | 0 | None |
| Tidal flooding in areas to the south of Boston, including Wyberton and Frampton | Warning area | 0 | None |
| Area at risk of river and tidal flooding in West Boston | Warning area | 0 | None |
| Area at risk of river and tidal flooding in North Boston | Warning area | 0 | None |
| South Forty Foot Drain in Boston | Warning area | 0 | None |
| Lower River Witham | Alert area | 37 | None |
| Wider area of the South Forty Foot Drain | Alert area | 26 | None |
| Far extent of Tidal Flooding from the Wash and Tidal Estuaries | Alert area | 12 | None |
| Tidal flooding of areas near the Witham Haven between Skirbeck and Hobhole Drain | Alert area | 0 | None |
| Tidal flooding of areas near the Witham Haven in Boston | Alert area | 0 | 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.
Boston is in the lowest radon 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).
Every 1 km square over Boston is in the lowest band: fewer than 1 in 100 homes are expected to be above the action level.
BGS/UKHSA Indicative Atlas of Radon in Great Britain, version 3. Check an address at UKradon.org.
Flood risk in the places around Boston
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 |
|---|---|---|---|---|
| Boston | 45,347 | under 0.1% | 100% | B |
| Fishtoft | 1,077 | 1.7% | 98% | C− |
| Kirton | 5,576 | 0.6% | 99% | C+ |
| Butterwick | 1,363 | 1.6% | 98% | C− |
| Sibsey | 1,520 | 0% | 30% | B |
| Sutterton | 1,068 | 33% | 67% | D− |
| Swineshead | 2,653 | 5% | 19% | D |
| Old Leake | 1,173 | 72% | 28% | D− |
Old Leake, 6.4 miles north-east, has the most homes at risk around Boston (72% at high or medium). Sibsey has none.
Get ready for what Boston 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.
- Boston’s warning areas include Tidal flooding in the East of Boston and surrounding areas and Area at risk of river and tidal flooding in West Boston.
- 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.
- Never walk or drive through floodwater: 30 cm of moving water can float a car.
- Move valuables, papers and medicines upstairs.
- Turn off gas, electricity and water if you’re told to.
- 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.
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 Boston
Does Boston flood?
The last flood the Environment Agency recorded inside the town was in January 2025. Under 0.1% 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 4.5% of homes are at high or medium risk from surface water, when heavy rain overwhelms the drains. Boston grades B for hazard risk against UK towns.
Which parts of Boston are at risk of flooding?
From rivers and the sea, the places the Environment Agency warns directly: Waterside properties between Town Bridge and Haven Bridge in Boston, Wider waterside properties between Grand Sluice and the Docks in Boston, Tidal flooding in the East of Boston and surrounding areas and Tidal flooding in the South of Boston and surrounding areas. Surface water can collect in low spots anywhere in the town. Check a specific address on GOV.UK’s long-term flood risk service.
When did Boston last flood?
The recorded flood outlines inside the town run from 1978 to 2025 (3 years); the largest was in 2013. Flood warnings have been issued for parts of the town since 2006, most recently on 6 January 2025.
Is Boston at risk of surface water flooding?
About 1.3% of homes are at high risk and 3.2% at medium risk from surface water, against under 0.1% 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 Boston?
Not by the atlas: every 1 km square over Boston is in the lowest band, where fewer than 1 in 100 homes are expected to be above the action level.
Are there flood warnings in Boston now?
No flood warning or alert was in force near Boston at 11 November 2026, 10:25. 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.