The National Trust said the project at Holnicote Estate in Somerset is the first of its kind for the UK.
A project to return rivers to a more natural state where they meander "like the branches of a tree" is being brought in to help wildlife and tackle flooding.
The National Trust said the project at Holnicote Estate in Somerset is the first of its kind for the UK and will allow rivers to flow through multiple channels, pools and shallow riffles as they would have done before human interference.
It differs from more conventional river restoration projects which bring back the bends or "meanders" in a single straightened stream, and aims to reconnect the water courses with their original flood plains.
It is hoped the scheme will reduce the frequency of flooding - which could become more common with climate change - by slowing the flow of water. It could help with other impacts of climate change such as drought by holding more water in the landscape, the Trust said.
And it could boost wildlife such as threatened water voles by improving riverside habitat.
Work has already begun to return a tributary of the River Aller, on the edge of Exmoor, to its original flow to allow natural river and wetland processes to develop across 10 acres of land.
If successful, it will be developed across a 33-acre site on the River Aller itself.
The approach, known as Stage 0 and based on successful projects in the US, will use diggers to move earth and recreate channels that allow the water's natural flow, mud and wildlife to rebuild a stream and wetland system.
And some habitat restoration will be "fast tracked" using wood debris and key plant species.
The creation of a more natural landscape will help a range of plants and animals, including 300 water voles released on the estate by the conservation charity in the past year.
It will allow a landscape which has been drained and intensively grazed in the past to become re-wetted and develop naturally, and the Trust said it will see how the habitat develops before making decisions on future management.
Ben Eardley, project manager for the National Trust, said: "Many streams and rivers have become disconnected from the surrounding landscape through years of land drainage and mechanised flood control.
"Conventional river restoration projects typically 're-meander' straightened streams, working on the assumption that these streams were single channelled before human interference.
"But there is strong evidence that prior to disturbance many watercourses naturally flowed through multiple branching channels, a bit like the branches of a tree."
He said that over hundreds of years people had simplified and concentrated rivers into single, straight channels which have been disconnected from the landscape, moving water rapidly down stream and providing no buffer against floods, droughts or the loss of topsoil.
He added: "With an increase in flooding and droughts predicted through climate change we need to make our landscapes more resilient to these challenges."
The scheme is being run in conjunction with "Interreg 2 Seas Co-Adapt" - a European programme covering England, France, the Netherlands and Belgium - and the Environment Agency.
It is also part of the National Trust's Riverlands project, where more than £14 million will be spent on seven river catchment schemes around England and Wales.