Photo: Stephen McKay · CC BY-SA 2.0Rivers or the sea put 8.9% of Grimsby’s homes at high or medium flood risk, more than in 95% of UK towns
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. Grimsby’s Hazard risk Grade is D: #51 of 61 in Lincolnshire.
What stands out about Grimsby’s hazards
From the Environment Agency’s maps and records and the BGS radon atlas, below.
What Grimsby 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
Grimsby grades D 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 Grimsby
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 Humber, the North Sea and the New Cut Drain. Surface-water risk is spread across the town, in dips, underpasses and along small streams, which is why more homes are exposed to it.
8.9% of Grimsby’s homes are at high or medium risk from rivers or the sea
The Environment Agency’s national map, allowing for defences. A further 16% 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; Grimsby has more than 95% of towns.
| # | Town | People | High or med. | |
|---|---|---|---|---|
| 1 | Oldham Greater Manchester | 110,722 | 0% | |
| 2 | Birkenhead Merseyside | 109,854 | 0% | |
| 3 | Dudley West Midlands | 64,277 | 0% | |
| … | ||||
| 89 | Lincoln Lincolnshire | 104,553 | 6% | |
| 90 | Maidenhead Berkshire | 67,391 | 6% | |
| 91 | Grimsby Lincolnshire | 85,915 | 8.9% | |
UK towns of 60,000 to 120,000 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.
9.9% of Grimsby’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 4.4% of homes are at high risk of surface-water flooding (a 1 in 30 chance or more each year) and 5.5% at medium risk: roughly 3,790 households. A further 13% face a low risk from surface water. That is more than 91% 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.
Grimsby has flooded in 2 recorded years since 1953, most of all in 1953
Every flood the Environment Agency has mapped inside Grimsby’s built-up area, newest first. The record is fullest for big river floods; small and surface-water floods are often missing.
- 2007June 2007: River flooding recorded8 hectares inside today’s built-up area
- 1953January 1953: The sea came in301 hectares inside today’s built-up area
Floodwater covered 301 hectares of what is now Grimsby in 1953, the largest flood the record holds here (January).
216 of Grimsby’s households today live inside the outline of a recorded flood.
Since 1953, the largest recorded flood inside the town covered 8 hectares.
No flood warning or alert is in force for Grimsby · 12 warnings in 20 years
The Environment Agency has 11 flood warning areas and 3 alert areas reaching into the town; warnings since the service began in 2006.
The warning area covering the most of Grimsby, Wider area at risk of tidal flooding from Immingham to Pyewipe, has not had a flood warning since 2006. Of the 12 warnings, 3 were for Tidal flooding in low-lying areas in Grimsby and 3 for Areas near to the New Cut Drain in the Wybers Wood and Willows Estate areas of Grimsby.
2013 had the most warnings (7); 2007 the most alerts (11). The most recent warning was on 12 January 2017.
Show the 14 warning and alert areas
| Area | Kind | Since 2006 | Now |
|---|---|---|---|
| Areas near to the New Cut Drain in the Wybers Wood and Willows Estate areas of Grimsby | Warning area | 3 | None |
| Tidal flooding in low-lying areas in Grimsby | Warning area | 3 | None |
| Areas near to the sea defences in Cleethorpes | Warning area | 3 | None |
| Wider area at risk of tidal flooding in Central Grimsby | Warning area | 1 | None |
| Wider area at risk of tidal flooding in the East of Grimsby and Cleethorpes | Warning area | 1 | None |
| Wider area at risk of tidal flooding in the West of Grimsby | Warning area | 1 | None |
| Wider area at risk from the New Cut Drain in the Wybers Wood and Willows Estate areas of Grimsby | Warning area | 0 | None |
| Wider area at risk of tidal flooding from Immingham to Pyewipe | Warning area | 0 | None |
| Tidal flooding in The Willows and Great Coates areas of Grimsby | Warning area | 0 | None |
| Area at risk from the furthest extent of tidal flooding from South Killingholme to Grimsby | Warning area | 0 | None |
| Areas near Stallingborough North Beck and Oldfleet Drain | Warning area | 0 | None |
| Humber tributaries | Alert area | 47 | None |
| Tidal flooding near the South Humber Bank from Barton Upon Humber to Humberston | Alert area | 23 | None |
| Far extent of Tidal flooding on the South Humber Bank | Alert area | 20 | 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.
Grimsby 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 Grimsby 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 Grimsby
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 |
|---|---|---|---|---|
| Grimsby | 85,915 | 8.9% | 16% | D |
| Cleethorpes | 29,660 | 27% | 11% | D− |
| Waltham | 6,204 | under 0.1% | 0.6% | B |
| Humberston and New Waltham | 14,861 | 4.7% | 4.3% | D |
| Healing | 3,201 | 0.4% | 0.5% | C+ |
| Laceby | 3,284 | 0.1% | 0% | B− |
| Holton le Clay | 3,823 | 0% | 0% | A |
| Stallingborough | 1,190 | 0% | 0% | A |
Cleethorpes, 2.4 miles east, has the most homes at risk around Grimsby (27% at high or medium). Holton le Clay and Stallingborough have none.
Get ready for what Grimsby 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.
- Grimsby’s warning areas include Wider area at risk of tidal flooding in the West of Grimsby and Wider area at risk of tidal flooding in Central Grimsby.
- 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 Grimsby
Does Grimsby flood?
The last flood the Environment Agency recorded inside the town was in June 2007. 8.9% 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 9.9% of homes are at high or medium risk from surface water, when heavy rain overwhelms the drains. Grimsby grades D for hazard risk against UK towns.
Which parts of Grimsby are at risk of flooding?
From rivers and the sea, the places the Environment Agency warns directly: Tidal flooding in low-lying areas in Grimsby, Areas near to the New Cut Drain in the Wybers Wood and Willows Estate areas of Grimsby, Areas near to the sea defences in Cleethorpes and Wider area at risk of tidal flooding in the West of Grimsby. 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 Grimsby last flood?
The recorded flood outlines inside the town run from 1953 to 2007 (2 years); the largest was in 1953. Flood warnings have been issued for parts of the town since 2006, most recently on 12 January 2017.
Is Grimsby at risk of surface water flooding?
About 4.4% of homes are at high risk and 5.5% at medium risk from surface water, against 8.9% 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 Grimsby?
Not by the atlas: every 1 km square over Grimsby 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 Grimsby now?
No flood warning or alert was in force near Grimsby at 7 November 2026, 21:28. 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.