Yes, in parts, and the river maps show only some of it. A small share of Isleworth lies in the river-and-sea flood zones. About one postcode in six is rated high on at least one flood measure. Only one flood is on record, and it was a long time ago. The Thames maps cover less than the full risk.
On the Environment Agency's river-and-sea flood maps, about 3% of Isleworth's postcodes are in flood zone 3, the highest-probability band. Another 3% are in zone 2, the medium-probability fringe outside it. The geography explains why the share is so small for a riverside town. The River Crane meets the Thames here, the Duke of Northumberland's River splits off it towards Isleworth Ait, and most of the town is on higher ground behind its stretch of the Thames. Isleworth is one of the few places where a duke has a river named after him running towards the flood map.
Surface water is the risk those zones leave out. It's rain that has nowhere to drain, and it can turn up well away from any riverbank. There's no separate surface-water figure for Isleworth here. It's counted in the postcode measures below, alongside rivers and sea.
The Environment Agency also models a future climate allowance. With it, the share of postcodes in a river-and-sea flood zone rises to about 7%. That's a modelled scenario for planning. It changes which streets are drawn inside the line.
Insurance is where this hits the buyer. Most of Isleworth should insure normally, but a home in a high-risk postcode can face a higher premium, a larger excess or a narrower choice of insurers. The practical check is to get a buildings insurance quote on the exact address while the survey is still being arranged. A quote tells you in an afternoon what the flood maps would take a week to explain.
The postcode-level measures cover more risk types, and the numbers grow. About 17% of Isleworth's postcodes are rated high on at least one flood measure, 21% medium and 41% low. Each postcode is counted once, at its worst rating on any of the measures. These shares overlap with the flood-zone figures above and shouldn't be added to them.
Counting homes gives a more useful picture than counting postcodes. In the Environment Agency's rivers-and-sea risk mapping, only 42 Isleworth postcodes carry any risk at all, and between them they hold 951 properties. Of those, 48 are at high risk, 46 of them homes, 17 at medium risk, 305 at low and 155 at very low. The rest of the town doesn't appear in that list because its rivers-and-sea risk is negligible.
The Environment Agency's modelled flood extents put well under 1% of postcodes in the high-probability extent, with or without defences counted, and about 3% in the low-probability extent. "Defended" in that model means a defence exists. It doesn't promise the defence will hold, and a seller using the word is describing the model. The only recorded flood is from 12 December 1965, when the main river burst its channel and there were no raised defences in the way.
The nearest tide gauge is at Portsmouth. Between 1962 and 2023 it recorded sea level rising by about 2 millimetres a year. That's a rate measured on the south coast, applied to a town on the tidal Thames. It's the best long record available, but it describes Portsmouth's past, not Isleworth's future.
Flood risk is Isleworth's weak spot. It's below average for a riverside town, with most of the risk concentrated in a minority of postcodes, so check the exact address.