Cambridge City Council worked with the Environment Agency to restore a fish passage at Sheep’s Green Local Nature Reserve (LNR), and transform the previously heavily silted and slow flowing channel that crosses it.
The works modified an existing culvert structure and were designed using natural ramps and pools to minimise the use of hard engineering on this important city centre wildlife site. The restored watercourse will benefit many species of plants and wildlife and also provide opportunities to observe fish close to the city centre.
The King’s Mill and Newnham Mill on the River Cam, at the northern end of Sheep’s Green are known to have existed since the Norman Conquest. Close to the historic centre of the city, the mills were once essential to the economy and development of Cambridge. However, impounding the River Cam to provide water for the mills’ wheels meant that the river was essentially cut off to fish movement.
Rivers provide vital habitats for plants and wildlife, and healthy fish populations help maintain a multitude of other native species. A variety of fish species can now migrate between the Newnham Mill Pool, via the Sheep’s Green nature reserve, and the upper River Cam by the Cambridge Canoe Club.
The increased flow is already clearing silt from the channel, providing spawning sites for fish such as minnow, chubb, dace and, it is hoped, wild brown trout.
Fish, including eels, which have suffered dramatic decline in their population, have already been observed using the restored watercourse and predatory bird species such as grey herons and kingfishers have quickly returned to take advantage.
Cllr Anna Smith, Executive Councillor for Streets and Open Spaces, said: “We are already seeing the effects of the project to restore the watercourse and fish pass at Sheep’s Green, with species returning to the site that have not been seen for some time.
“Sheep’s Green is one of many Local Nature Reserves in the city that not only offer places to enjoy nature and give much-needed habitats to native species in the city, but can also play a role in lessening the effects of extreme weather by, for example, providing areas for the run-off of water after heavy rainfall.”
Ellis Selway, Geomorphology Technical Advisor for the Environment Agency, said: “This has been a fantastic opportunity to work in partnership with the city council to deliver environmental benefits that also generate a legacy for the community. This is part of the Environment Agency's commitment to deliver an environment programme which makes a difference to wildlife and people.
“To see the re-connection of fish populations which been isolated by the historic use of the river for centuries and see fish ascending up the pass is fascinating. Our aim is to achieve environmental benefits by using near natural solutions to historic modification of the river where possible.”
The project is linked to a similar scheme at Byron’s Pool LNR in Trumpington, where the council has installed a natural bypass channel to the weir. This latest project means fish now have access past the two mill pools upstream to Byron’s Pool and beyond.
Image: New sluice and pool at upper end of the newly constructed fish pass.
The Local Nature Reserves (LNRs) in Cambridge are for both people and wildlife. The designation of these reserves helps to protect some of the best wildlife habitats and geographical features across the city, whilst making an important contribution to the UK’s biodiversity. The reserves provide an opportunity for people to study, learn about and enjoy nature on their doorstep. For more information visit: https://www.gov.uk/government/publications/biodiversity-2020-a-strategy-for-england-s-wildlife-and-ecosystem-services and http://lnr.cambridge.gov.uk/
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