A scheme to flood 300 acres of farmland in Lincolnshire could still go ahead, despite being turned down by planners.
The Environment Agency wants to allow the sea into Donna Nook, North Somercotes, as replacement wetland for habitats lost to flood defences nearby.
But East Lindsey District Council rejected the plan in June following strong local opposition to the loss of land.
Now the agency has confirmed it will appeal to the Planning Inspectorate.
A spokesman for the Environment Agency said it was obliged to replace wetland habitat lost to the wider Humber estuary flood defence programme.
"The Donna Nook site, in the outer Humber Estuary, has been identified as the most suitable site to develop this compensatory habitat.
"We were disappointed that East Lindsey's Planning Committee did not approve our planning application to implement this work.
"Protecting the homes, land and livelihoods of the many thousands of people who live and work on the Lincolnshire and Humber coastline is important, and therefore it is right that we should appeal this decision."
The district council said it was aware of the Environment Agency's decision and would now consider the best way to defend the appeal.