The Dogger Bank sandbank in the middle of the North Sea is set to become Britain's latest marine protected area.
Dogger Bank is an important habitat for crabs, brittlestar starfish, jellyfish, clams, plaice, sole and sand eels.
A 12,000 sq km (4,600 sq mile) area has been submitted to the European Commission to be included in a European network of nature protection sites.
As a result it must now be protected from damaging activities which could harm wildlife and habitats within it.
The Department for Environment, Food and Rural Affairs (Defra) said the move should not jeopardise plans to develop Dogger Bank as a prime area for offshore windfarms.
However, windfarm plans may have to be modified after being assessed for their environmental impact.
Dogger Bank lies in the offshore waters of the UK, the Netherlands and Germany.
The government said it was the largest marine site to be submitted by a European Union (EU) country and the UK section would link up with existing protected areas in German and Dutch waters.
Natural Environment Minister Richard Benyon said: "The thousands of species and habitats in our seas need just the same protection as those on land.
"The Dogger Bank is home to a fantastic array of sea life and habitats, and thoroughly deserves special protection.
"This marks a major step towards achieving our commitment to create an ecologically coherent network of marine protected areas."
The public is being consulted on three more SACs, the Wight-Barfleur Reef in the English Channel, and the Pisces Reef Complex and Croker Carbonate Slabs in the Irish Sea.
A further consultation by government conservation agency Natural England has also started on a reef site at Studland to Portland off the Dorset coast.
Proposals for a series of marine conservation zones, which will sit alongside the existing European designated sites to form the network of protected areas required under the 2009 Marine Act, will be presented for review in September.