Checks carried out after installation identified concerns about several of the 44-tonne prefabricated beams in the bridge structure last year.
Hertfordshire County Council and main contractor Tilbury Douglas carried out a series of tests and decided that all 13 prefabricated beams will be replaced.
After the defective ones are removed, new beams and a deck will be installed, to ensure that the bridge is constructed to meet the required specification.
The new A602 road and bridge are expected to now fully open by summer 2023 as part of a £20m improvement project.
Phil Bibby, Executive Member for Highways and Transport at Hertfordshire County Council said: “We are pleased that the solution has been agreed, to ensure that the road and bridge are constructed as intended. We welcome the patience of the community and road users until the road opens in summer 2023.”
The council added in a statement: “Hertfordshire County Council is in contract with Tilbury Douglas Construction Limited (TDCL), and TDCL with their supply chain are responsible for constructing the bridge to the required specification.”