The Cuttlebrook, a tributary of the River Thame which is probably best known as the watercourse that runs through the popular eponymous nature reserve in the centre of Thame, the Cuttlebrook Nature Reserve, is receiving some concerted habitat improvements and conservation efforts this year. RTCT has been working in collaboration with the Cuttlebrook Conservation Volunteers, the active community group who, for over 30 years, have worked to ensure that this special site continues to be a thriving hub for wildlife.

The Cuttlebrook, where it runs through the nature reserve, is perhaps not typical of the appearance of a quintessential chalk stream with gin-clear water and a gravel bed. However, it is influenced by the cool (temperature regulating) groundwater from the chalk of the Chilterns, which is an important sustaining attribute for the  Brook’s wildlife in a warming world. The Brook is one of the only chalk stream tributaries in the Thame which does not feature a sewage treatment works (i.e. it does not receive sewage effluent), meaning it has relatively good water quality (see map below). Lastly, the Brook and the reserve are an important greenspace for residents of Thame, and further afield – providing physical and mental wellbeing benefits. These attributes make the Cuttle Brook deserving of conservation efforts. Through a variety of restoration, from vegetation management, through in-stream works and scrapes to fish passage improvements, we are addressing some key habitat degradation issues in the Cuttlebrook.

The absence of a sewage treatment facility in the Cuttlebrook sub-catchment is a rarity within the Thame catchment, which has 33 sewage treatment works within the catchment. In fact, only 4 of the 20 sub-catchments in the Thame catchment are free from the influence of sewage effluent, making the Cuttlebrook an exceptional opportunity for targeted restoration.

Tackling Barriers to Fish Passage on the Cuttlebrook

When developing our strategy for habitat restoration on the Cuttlebrook, improving the brook for fish was a high priority. Surveys conducted by RTCT uncovered two obstructions in the lower reaches of the brook, a dilapidated concrete weir downstream of the reserve and a concrete weir housing a pipeline at Greysmead upstream of the nature reserve, both of which act as barriers during low flows that prevent fish from freely migrating to find food, shelter and areas for spawning.

Work on the Greysmead barrier has already been completed. Notched fish ‘baffles’ have been installed, narrow boards made of recycled plastic which are placed downstream of the obstruction. The height, location and size of the notch between the baffles have been designed to enable the passage of fish during times when the water levels in the brook are low without having an impact on the hydrology of the brook during medium to high flows. The baffles slightly raise the water level behind them to drown out the existing weir and give fish the ability to swim upstream.

The second fish pass issue in the Cuttlebrook is a deteriorating concrete weir downstream of the nature reserve adjacent to Rycote Meadow.  RTCT will work with an external contractor to remove the barrier and naturalise the channel, reducing impoundment and therefore sedimentation and restoring fish passage during lower flows. The work is fully permitted, funded and contracted. Weather permitting, we plan to remove this barrier in early 2025.

Creating new wetland habitat along the Cuttlebrook

The fields adjoining the Cuttlebrook offer an excellent opportunity for increasing biodiversity through wetland habitat creation. We plan to construct two shallow scrapes within the reserve which will hold floodwater seasonally. Wetland scrapes support a wide range of wildlife, from wetland plants, to aquatic invertebrates to wading birds. After construction, in early 2025, these news scrapes will provide invaluable food and refuges for wildlife.

The two new scrapes that are planned by RTCT will complement the work by the Conservation Volunteers that was delivered in Summer 2024. In Rycote Meadow, just across the Oxford Road from the nature reserve, Thame Green Living, Cuttlebrook Nature Reserve and Thame Town Council had been working together to improve the rare remnant floodplain meadow found here with a seasonal scrape and a new hedgerow full of native species, which has been planted which will benefit wildlife, particularly birds and insects. The next steps of this sister project will be to construct a fenced footpath through the meadow which protect the new habitats from disturbance.

Improving the Instream Habitat of the Cuttlebrook

The physical channel and instream habitat of the Cuttlebrook is our final focus for upcoming improvements. As the stream flows through the reserve there are overwidened, artificially modified stretches and inconsistent bed levels which has led to thick silt deposits. The thick sediment on the river bed has smothered the gravel bed underneath, degrading habitat for aquatic macroinvertebrates and spawning areas for the existing diverse fish populations.  

To improve in-stream habitat diversity, RTCT has designed and sought permission from the Environment Agency for the Cuttlebrook Conservation Volunteers to complete vegetation clearance of instream obstructions and construct a series of in-stream structures from woody materials. The structures will help establish a more diverse riverine habitat exposing the gravel beds and increasing the diversity of microhabitats within the river channel.

The Cuttlebrook Conservation Volunteers have already been hard at work removing riparian vegetation and sourcing local materials which will be used as natural construction materials. Selective thinning out of riparian trees has the added benefit of opening up sections of the brook to sunlight, encouraging the growth of aquatic plants. Some of the structures will also be built as revetments to prevent erosion of the banks, an issue which is exacerbated by people and dogs using the banks. With all these improvements planned, this stretch of channel has the potential to offer even more habitat for spawning fish and an array of aquatic invertebrates.

While the Chalk Stream Strategy on the Cuttlebrook has already seen some exciting progress, this is only the beginning of the journey to enhance this rare chalk stream and its surrounding habitats. The River Thame Conservation Trust, in collaboration with the Cuttlebrook Conservation Volunteers and other partners, is committed to continuing this vital work. From improving fish passage and creating wetland habitats to enhancing the stream’s physical structure, every step brings us closer to a healthier, more biodiverse future for the Cuttlebrook.

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