The footbridge at the Vineyard Road end of the canal was discovered in a precarious position today.
Newport Mayor Peter Scott said he has reported the act of vandalism to the police and encouraged anyone who may have information to call 101 and report it.
He said: "This kind of thing makes me so angry.
"What is it with some people? Why would anyone want to vandalise the wooden bridge at the top of the canal? Just wanton vandalism.
"If you have any idea which total fools did this please call the police on 101."
Alternatively, contact Crimestoppers anonymously on 0800 555111 or at crimestoppers-uk.org