Police were called after four cabin boats vanished from moorings near the Norfolk Mead hotel at Coltishall on the River Bure.
It was initially feared that the craft, unoccupied at the time, had been stolen from the public moorings some time during Saturday night.
Police were joined by Broads Authority staff in a search down river and one of the boats was quickly found stranded on a mud bank.
The others were also located downstream their mooring ropes apparently having been untied by vandals.
A police spokesman said: 'We would like to hear from any witnesses who saw what happened and ask them to call us on 101.'
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here