A police spokesperson told the Herald they had had a report about the video and were assessing it.
SPCA inspectorate team leader Pip Lamb said the video was "concerning".
"This sort of behaviour is extremely irresponsible and could result in injury to the dog, and may constitute an offence under the Animal Welfare Act."
Lamb said anyone who saw the dog being pushed off the bridge or has information about the people who did it should contact SPCA's Gisborne Centre on (06) 867 9463 and follow the extension instructions to report a welfare concern.