The Babingley, one of only 200 chalk rivers left in the world, is undergoing a clean-up with the aim of making a better habitat for fish and other wildlife.
The work is being undertaken by the Norfolk Rivers Trust, supported by environmental solutions company Salix.
The Babingley rises from chalk springs above Flitcham and Hillington, meanders through the Sandringham estate and joins the sea through Wootton Marsh into the Great River Ouse.
The river provides habitat for eels and migratory freshwater fish, including bullhead and brook lamprey, as well as waterway mammals, like water voles and otters.
It’s also important for birds like buzzards, barn owls and kingfishers, and invertebrates like damselflies and dragonflies.
Jonah Tosney, Norfolk Rivers Trust’s Nine Chalk Rivers project manager, said: “Despite centuries of modification, the upper Babingley remains one of the finest, clearest and cleanest stretches of chalk river in Norfolk.
“It is particularly special as there are now only around 200 true chalk streams left in the world, of which 15 per cent are here in Norfolk.
“Rainwater soaks through chalk ground and, cooled and filtered by its journey through the chalk, emerges at a constant temperature and with a clear and alkaline quality.
“This makes chalk rivers become England’s rainforests, providing a perfect, gentle habitat in which everything grows abundantly – insects, water plants, fish, crayfish, birds and mammals, including the critically endangered water vole.
“Sadly the World Wildlife Fund’s recent State of England’s Chalk Streams report says that 77 per cent of our chalk streams are failing to meet the Good status required by the EU’s Water Framework Directive.
“The Babingley has been straightened and controlled in places using steep man-made banks and weirs. It also suffers from silt build-up from local roads and farms.
“The weirs back up water, slowing the flow and ponding the river. They also make fish passage difficult, as water surges through a narrow opening, making life difficult for less able swimmers such as bullhead and stone loach.
“Where the channel has been straightened and lowered, a more uniform habitat has been created which can be exploited very well by a small number of species but will exclude many other associated with chalk rivers.
“Work on our river restoration project here on the Babingley at Hillington is being carried out by bioengineering specialists Salix and includes removing an old weir and restoring more natural channel shapes and flow patterns.”
Chris Mackintosh-Smith, project manager for Salix, says: “We are using local timber and gravel for channel re-shaping, narrowing and deepening, offering a more diverse range of passages and variations in water movement.
“As well as creating riffles and eddies in the water, the wood and the gravel provide places for the fish to hide from predators and seek shade from the sun. And they offer another habitat layer for invertebrates, which in turn provide food for the fish.
We have also removed the wing wall and lowered a sill at a brick weir to improve river continuity and make it easier for fish to pass through.”