One of the largest wetlands left in southern England is being designated by the government as a site of international importance.

But the Royal Society for the Protection of Birds (RSPB) says designation is not enough a site already recognised as one of the jewels in Britain's wildlife crown.

The wetlands, Pevensey Levels in East Sussex, are home to 70% of all the species of flowering aquatic plants found in Britain - and to the leech.

More help needed if Ramsar is to work

The Levels are a large area of low-lying grazing meadow, criss-crossed by ditches. They also harbour 21 of Britain's 38 dragonfly species and a huge range of other wildlife.

The area is one of only two sites in Britain for the fen raft spider, and is well known for its birds.

In the winter especially, it has vast flocks of wildfowl and waders such as lapwing.

The Levels are designated as a site of special scientific interest (SSSI) and part is also a national nature reserve.

More protection

But the levels are now being declared a site designated under the Ramsar Convention, named after the Iranian town where it was adopted in 1971.

The Convention on Wetlands of International Importance now covers more than 900 sites worldwide, including 133 in the United Kingdom.

Speaking at a ceremony to mark the designation, the minister for fisheries and the countryside, Elliot Morley MP, said the levels were a very special place for wildlife.

He said: "The government is happy to accept the obligation to ensure that the site continues to be managed in a way which conserves and enhances its value for wildlife."

The government's wildlife advisors, English Nature, are responsible for much of the levels.

English Nature's chairman, Baroness Young of Old Scone, said the conservation of the levels was "a tremendously successful example of the private and the public sectors working in partnership".

"Disastrous decline"

But the RSPB - which Baroness Young used to head before joining English Nature - said the levels' Ramsar designation "will do little to stop the disastrous decline in wading birds".

It welcomes the government's action in designating the levels, but urges better protection and management as well.

The RSPB says the levels used to support 16,000 wintering waterfowl, but that many birds have vanished in the last 20 years.

In the spring, it says, the fields are too dry to allow wading birds such as snipe and redshank to raise and feed their chicks.

Water levels began dropping 30 years ago when pump drainage was introduced.

The RSPB says there is no funding to support the water management plans that have been drawn up.