One third of the lock keeper's cottages along the River Thames are to be sold off or let out to save money.
The Environment Agency said it would sell 10 of its 57 properties along the river as part of efficiency savings.
A further 12 properties will be rented out privately as they are no longer needed for "operational reasons".
The agency said lock keepers will remain in work. But some people have expressed concerns that a presence will not be maintained 24 hours a day.
Eileen McKeever, the Thames waterways manager at the Environment Agency, said: "We need to operate the river as efficiently as we can, making sure we are using public money wisely.
"We will not be moving anyone out of a house until they have another suitable house to go to - we will not be making people homeless.
"We will still man locks to assist boaters with passage through the locks. We plan to have more staff on duty during the busiest times throughout the summer."
Of those lock house that will be sold, one is in Oxford, two in Maidenhead, five in Surrey and two in Buckinghamshire.
People were living in the properties and two were rented privately, the Environment Agency said.
'Modernise working practices'
The agency would discuss with them about moving to other accommodation, and the houses would be sold over five years - with the money going into projects on the river, a spokesperson added.
But resident Gillie Bolton from Old Windsor, Berkshire, said she was "horrified" that the Environment Agency was "not taking notice of last year's catastrophic floods".
"There are going to be problems in the future," she added.
Ms McKeever added: "We are aware that this is a very emotive issue for lock keepers and their families, but we have been running the river in the same manner for 40 or 50 years and we need to modernise our working practices.
"There will be no impact on how we manage flood risk."