The seabed off West Sussex is set to be leased from the Queen by councils looking to restore marine habitat.
Adur and Worthing councils say it could lead to the creation of a Sussex Bay marine park along the entire length of the West Sussex coast.
The Crown Estate, which manages the land on behalf of the Queen, owns the sea bed to a distance of 12 nautical miles (22km) off the coast.
The councils say the measures will protect habitats such as kelp forests.
A bylaw agreed earlier this year by the Sussex Inshore Fisheries and Conservation Authority excludes trawling from a 117 sq mile (302 sq km) area.
The Crown Estate is now in discussions with the councils to allow the authorities and their partners to invest in kelp forests.
Forests of kelp once stretched along 25 miles (40km) of the West Sussex coastline from Selsey to Shoreham, and extended at least 2.5 miles (4km) seaward.
The kelp forest provided habitat, nursery and feeding grounds for seahorses, cuttlefish, lobster, sea bream and bass.
It also locked up huge quantities of carbon, improved water quality and reduced coastal erosion by absorbing the power of ocean waves, campaigners said.
They said kelp had been ripped from the seabed by dragging nets from trawling vessels.
Worthing Borough Council's executive member for Digital and Environmental Services, Edward Crouch, said, "This is a potential game-changing project which would help us cut carbon emissions, restore beautiful marine and estuarine habitats."