This is based on ongoing surveillance in the area, veterinary risk assessment, and expert ornithological advice about the area most at risk, in accordance with the Avian Influenza (H5N1 in Wild Birds) (England) Order 2006.
Highly pathogenic H5N1 was confirmed in three wild mute swans in the area on 10 January and to date there have been a total of 10 wild mute swans confirmed with the disease. The last case was a mute swan found dead on 29 January and confirmed on 4 February.
Acting Chief Veterinary Officer, Fred Landeg, said: "Our active surveillance and sampling in the area has provided evidence that the virus has been confined to mute swans and at a very low level. H5N1 appears to have been present in the area for about two months, during this time we have seen only a few deaths in the mute swans.
"We have no evidence of the virus being present in healthy live mute swans or in other species of wild birds. There is no evidence of disease spreading to domestic birds. On this basis we have today merged our Control Area and Monitoring Area to form a single Monitoring Area.
"It is timely to remind everyone that the UK remains at a constant low level of risk of the introduction of highly pathogenic H5N1, with a slight increase during winter and spring migration. I therefore urge all bird keepers to remain vigilant for signs of disease and take measures to isolate kept birds from wild birds."
The Wild Bird Monitoring Area must remain in place for at least 30 days following the collection of the last positive sample.