The incident happened at around 4pm on Sunday 26 June, upstream of Clifton Bridge, near to the RSPCA rescue centre.
The dog, described as looking like a brown Staffordshire Bull Terrier/Labrador cross, or an American Staffordshire Terrier, attacked the boy’s older brother first by pulling at his t-shirt. The owner then put the dog on a long lead but it then went for the three-year-old boy, biting him on the chest and shoulder.
Acting on information received from members of the public, police officers have carried out a number of searches to locate the owner of the dog, but so far, he has not been traced.
Investigating officer, PC Wesley Cooper said: “I would like to thank the members of the public who have come forward with information to assist the enquiry so far. Unfortunately, we have been able to trace the owner.
“A small child and his family have been deeply upset by this incident and I am issuing a renewed appeal for information. Anyone who knows the owner of a dog matching this description, which is walked on a long lead or off its lead in the York area, is urged to come forward.
“Better still, I urge the owner of the dog to search his conscience and identify himself to police.
Anyone with information is asked to contact PC Cooper on 0845 60 60 247, quoting reference 12110105980.