Work costing £1.2m is being carried out on a jammed river sluice on the River Nene in Cambridgeshire.
The Environment Agency is refurbishing Dog in a Doublet sluice and lock downstream of Peterborough.
The lock will be closed to boats for just over a week in October to replace the electrical operating system and to prepare to make it automated.
Dog in a Doublet sluice, built in 1937, forms the upstream limit of tidal defences for the River Nene.
It also controls upstream river levels.
Environment Agency project manager Elisha Tafirenyika said: "At present, the sluice is not fully operational because the north sluice is jammed and is in a deteriorating condition."
The Environment Agency said it had timed the closure to coincide with the end of the boating season to try to minimise disruption to river users.
Mr Tafirenyika said: "If the sluice were to fail, its tidal location would cause the upstream channel to become saline preventing water abstraction for irrigation, causing potential damage to the neighbouring Site of Special Scientific Interest and preventing us from being able to control river levels for navigation."
The work is expected to finish by January 2011.