WARDENS were on high alert today and patrols stepped up after three dead swans from Abbotsbury were found to have bird flu.
The mute swans were found to have been carrying the lethal H5N1 strain of the virus during routine tests.
Swannery site manager John Houston said that the outbreak was likely to have been caused by a wild bird flying on to the site.
Now the swannery is sealed off within a bird control zone stretching 20km from Abbots-bury to Portland Bill.
Swannery staff are stepping up patrols to look for any other ill and dead birds. They are ready to alert the Department for Environment Food and Rural Affairs (Defra) for urgent testing if they find any.
Wardens in Weymouth's nature reserves have also been told to remain extra vigilant for signs of the deadly bird flu virus spreading.
Extra patrols of Radipole Lake Nature Reserve and Lodmoor Country Park reserve will be carried out in the next few days.
Defra confirmed that the swans had the deadly H5N1 strain, but ruled out any cull of the swans or wild birds.
Mr Houston, the general manager of Abbotsbury Tourism, said: "When I first heard I was shocked and disappointed but now that it's here we're going to manage and deal with it and limit the effect on swans and staff.
"Hopefully we will see it through quickly and be able to reopen to the public and have a decent season."
A member of staff found the three swans on Monday. Defra performed routine test on the birds and told Abbotsbury Swannery managers of the results 48 hours later.
Staff at the swannery have also been tested for the virus by the Health Protection Agency, but Mr Houston said they had been reassured there is very limited danger to employees because the site is open access with no confined exposure.
All poultry keepers on the British Poultry Register are being notified, and the European Union Comm-ission has been informed.