The Environment Agency is preparing to install a "demountable" barrier to close off a flood-prone Fenland road.
The "robust" road block will replace sand bags that are routinely placed across the A1101 Welney Wash Road when the area floods.
The authority will first seek public advice on the best time to close the road to allow work to start in 2021.
It is the final phase in a £27m scheme to strengthen the banks of the Ouse Washes reservoir over four summers.
The A1101 Welney Wash Road crosses the 30km-long (19 miles) reservoir near the village of Welney, on the Norfolk-Cambridgeshire border.
When water reaches a predetermined level, highways officials at Norfolk County Council close the road.
Work needs to be carried out between July and October to avoid disturbing overwintering and breeding bird populations.
The Ouse Washes is one of the largest remaining areas of lowland wet grassland in the UK and is identified as a Site of Specific Scientific Interest (SSSI).
Construction is expected to take 14 weeks, requiring the closure of the road for about six to eight weeks.
The Environment Agency is asking the public to suggest the best window in 2021 in which to do this.
Project lead Nicola Oldfield said the barrier was a "vital part" of the agency's plan to maintain the reservoir and protect the local environment.
"We appreciate that closing the Welney Wash Road will have considerable impact on the local community," she said.
"We want to reduce that impact by working with residents and businesses to identify the most appropriate time of year to close the road."
An online public consultation will be available from 12 March.