Yes, Olympic Park has a real flood risk, and it comes mainly from the river. About a third of the area lies in a river flood zone. Very little of it is in the highest-risk band. The river has overflowed onto this ground before. For a buyer, the flood question here is about which edge of the risk a particular flat is on.
On the Environment Agency's river-and-sea mapping, about 35% of the area's postcodes are in flood zone 2 and about 1% are in flood zone 3. The two zones don't overlap. Zone 3 is the higher-probability core, and zone 2 is the medium-probability band around it, so most of the exposure here is in the outer band. The Environment Agency's records list 80 flood events across the area. The most recent was in December 1947, when the main river overflowed its channel at a time when it had no raised defences. In those days nobody had yet planted meadows along its banks.
Looking ahead, the Environment Agency's climate-adjusted mapping puts about 37% of postcodes inside the flood zone. That is slightly more ground than the present-day zones cover, and it is a modelled allowance for wetter decades to come.
On a separate postcode-level measure, which counts a postcode if it rates on any one of several flood indicators, surface water included, about 6% of postcodes rate high on at least one, about 6% medium and about 17% low. One postcode can carry several indicators, so this measure and the river zones above are separate ways of looking at the same ground and should not be added together.
Counting buildings gives a smaller and more useful picture. The Environment Agency's rivers-and-sea assessment lists 756 properties in postcodes carrying some risk, and only those postcodes appear in the count at all. Of those, 7 properties are at high risk, 3 at medium, 77 at low and 29 at very low, and none of the high-risk properties is a home. Seven buildings is a small enough number to check by name. Putting the exact address into the Environment Agency's long-term flood risk service tells a buyer whether their flat is one of the few on that list or one of the many that are not.
About 1% of postcodes fall within the high-probability flood extent where the Environment Agency's model shows no defence, and a smaller share where it shows one. "Defended" here only means a defence appears in the model. It says nothing about how that defence will perform on the worst night of the decade. A defence lowers the odds of flooding without making a home dry.
For insurance, a flat on an upper floor in zone 2 is usually a different conversation from a ground-floor home with a door onto the same street. Insurers price the specific building and floor as well as the postcode. Anyone buying at ground level here should get an insurance quote early, because that is where the risk turns into a monthly cost. Before the Games, the whole site's soil was washed clean; the river could still have a go at it without permission.
The nearest tide gauge with a long record, at Portsmouth, measured sea level rising by about 2 millimetres a year between 1962 and 2023. That is a measured past rate at a gauge a long way from the Lea, and it describes what has already happened.
Olympic Park's flood risk is a real weakness. A buyer here cannot assume the water will stay where the meadows were planted for it.