"Leptospirosis may be suspected if your dog has had any contact with rats or stagnant water and displays clinical signs of vomiting,lethargy and diarrhoea,"the RSPCA said.
Two of the recently deceased dogs had frequented Ward Park on Devonshire Street in Surry Hills,according to a Facebook post by the Potts Point Veterinary Hospital.
"It has been suggested that the light rail building works in Surry Hills has interfered with some underground pipes,forcing rats and or contaminated water to the surface of parkland,"the post added.
Sydney's growing rat population has become the prime suspect for the outbreak.
University of Sydney lecturer Dr Christine Griebsch,from the School of Veterinary Science,said it was"early days"and the source of infection or strain of bacteria was still unknown,but that the University's investigation into the situation would probably begin with rats.
"We have more rats in Sydney than in the past due to recent reconstruction,"Dr Griebsch said."Rats are more prevalent in the outside environment now because they have been disturbed."