The Environment Agency is removing about 5,000 tonnes of silt from a Lincolnshire river to try to prevent nearby homes from flooding.
The work is being carried out on the River Welland to reduce the risk of flooding to 200 homes in Stamford.
Floating machinery is being used to remove the silt, which can reduce the rate of flow and the volume of water a river can hold.
The silt will be dried and used on farmland as a soil improver.
Glyn Davis, from the Environment Agency, said: "A build-up of silt can reduce both the rate of flow and the volume of water the river can hold. Together, these can combine to increase the risk of flooding during prolonged heavy rainfall.
"The Environment Agency is carrying out this de-silting work to maintain the river's water-carrying capacity and protect people and property in Stamford against flooding."
The work is expected to be completed next week.