Plans to build more than 200 homes on Poyll Dooey have been branded unacceptable by a local conservationist.
Dr Fiona Gell says the salt marsh is a natural flood plain protecting Ramsey during high tides and river flooding, and should be protected.
It's also home to various birds and local plant species.
She says Poyll Dooey is the second biggest salt marsh on the Island and is one of the best at absorbing carbon from the air.
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