The cost of a tidal barrier being built in Somerset is likely to rise by millions of pounds.
The Bridgwater project's price tag could increase by £10m or more, a Somerset County Council report shows.
Due to be completed in 2024, the flood defences aim to protect 10,000 homes from floods for the next 100 years.
Estimated costs rose from £60m to £70m after "getting firmer information on costs", Sedgemoor District Council's corporate director said.
Brian Smedley, Bridgwater Town Council leader, said the council had not yet been told what the extra costs are.
He wanted to ensure the project remained of a high standard so it could meet the needs of 11,000 Bridgwater homes and businesses and "to safeguard vital rail and road links".
Councillor Leigh Redman, of the county council's Labour group, called for the plans to move forward as quickly as possible "to prevent any further increase in costs".
Doug Bamsey, corporate director of the district council, said added costs were due to improving downstream flood defences and raising river banks.
He argued the price hike is "not extraordinary" and said "we have to have a robust scheme".
Mr Bamsey admitted the cost "might go up more, but equally the benefits are going up. You have to balance the benefits."
Bridgwater's council has been calling for a bypass to the town and Mr Redman said he still hoped this could be incorporated in the barrage.
The barrier will be built near Express Park, in north Bridgwater, and could provide sufficient water storage to handle a repeat of the flood crisis of 2014.
When finished, the structure will be 20m (65ft) high and 55m (180ft) wide, with a central pier and two piers supporting either side.