The handrails of the bridge suffered some damage and some concrete has peeled off, naval sources said. Traffic was held up for two hours after the incident.
The dredger 'Bhagavati Prem' was engaged by the navy for undertaking the extension work of the South jetty since the past few days, sources said.
According to the Navy, the dredger drifted towards the bridge due to tidal action.
A Defence press release said the freak accident took place about 11:20 AM and the dredger, employed by Cherian Varkey Construction Company Private Limited, went out of control and was swept away in a strong flooding tide.
Public Works Minister Ibrahim Kunju, who visited the spot, told reporters that a meeting will be called to assess the damage to the bridge, which connects Ernakulam with Wellington Island.