The puppies are thought to have been alive for less than 24 hours and were found with their umbilical cords still attached.
Construction workers at the West Midlands Metro site at Park Lane West in Tipton noticed a suspicious package floating in the water near Mission Drive on Monday morning.
The men notified the RSPCA after they pulled the bag from the water and found three dead puppies wrapped in white dishcloths, along with various plastic bags and a ‘Mamia’ nappy box inside.
RSPCA inspector Claire Davey collected the puppies and took them to the charity’s Birmingham Animal Hospital, where they were identified by a vet as two males and one female.
It wasn’t possible to tell whether the pups, thought to be Staffordshire Bull terriers, were alive when they were put into the bag, although all three appeared to be healthy.
The possibility that they may have been stillborn has not been ruled out.
Ms Davey said: "It’s absolutely heartbreaking to see very young animals dumped like this in such a cold and heartless way; these tiny, vulnerable pups still had their umbilical cords attached, so they were extremely young, probably no more than 24 hours old.
“It’s not clear whether they died during birth, of natural causes, or if something more sinister has happened, which is why I’m very keen to establish exactly how they came to be found in these appalling circumstances. We are also very concerned about the welfare
of their mum and any other litter mates.”
“I’d also like to extend my thanks to the construction workers who very kindly called us and were understandably shocked and upset by what they found.
“Anyone with information about the puppies can contact the RSPCA’s inspectorate appeal line, in confidence, on 0300 123 8018.”