A number of glass panels in the collapsible structure on the Old Bridge have been broken in recent days.
The bridge is part of the €40 million flood defence scheme for the town and the glass side walls can be lowered when river levels are particularly high to allow water flow over the bridge.
Previously vandals had caused similar damage to the bridge.
Local Sinn Féin Councillor Catherine Carey says the time has come to take action to prevent these attacks.
