Isles of Scilly vet Dr Heike Dorn is advising islanders and visitors to avoid walking their dogs on the Garrison after more than 20 were struck down with vomiting and diarrhoea.
Heike told This is Scilly that the situation is improving, but lots of dogs "had the s**ts" after being walked in the popular spot.
"They only need to sniff on something after an ill dog has sniffed there," she said.
"It's a virus or bacteria, it's hard to tell which. The best thing to do is avoid going where the problem is, and that is the Garrison."
Heike advised dog owners to stay away from the affected area for around two weeks.