Local authorities in England approved 13 developments in 2006/7 against Environment Agency advice on the risk of flooding, a report has revealed.
Many parts of the UK were left under water in the summer floods
These included plans for housing, roads and caravan parks in areas of the highest flood risk, the agency said.
It said some of the developments could "put life and property at risk".
But the Development and Flood Risk annual report showed decisions were made in line with flood-risk advice in 96% of cases where the agency objected.
This was up from up from 95% in the previous year.
Flats and houses
Environment Agency chief executive Baroness Young said seven of the projects approved against agency advice were in areas of the highest flood risk, which was "unacceptable".
She identified these as including 10 bungalows in Mablethorpe, Lincolnshire, plans for 18 homes and roads and a scheme to convert farmland to a caravan site, both in Chapel St Leonards, Lincolnshire, and construction of a new access road in Stowmarket, Suffolk.
Other plans passed despite concerns raised by the Environment Agency over potential risks of flooding by surface water run-off included an application for 23 houses and 78 flats in Barnet, north London.
Over the last six years, local planning authorities have increasingly heeded Environment Agency advice and avoided building in areas at high risk of flooding.
But Baroness Young said of the developments where advice was ignored: "If these major developments go ahead, they could put life and property at risk and bring misery to occupiers."
She said this summer had exposed the damage that flooding can cause.
"The right decisions about the location, design and nature of development must be made to protect people and the environment - especially in the face of climate change," she said.
She concluded that although flooding cannot be stopped, "inappropriate development in areas at high risk of flooding" could be avoided.
Earlier this week she warned that climate change meant the UK was likely to face more flooding, as well as droughts, coastal erosion and loss of biodiversity.