The Chalgrove Brook is one of the very few chalk streams that run into the Thame Catchment off the Chilterns escarpment, and is especially noteworthy for containing the only known population of Brown Trout. The Lewknor Brook flows into the Chalgrove Brook below Cuxham with the combined water course continuing through Chalgrove and Stadhampton to join the Thame just above the bridge at Chiselhampton. Another small stream, Pyrton Brook, meets the Chalgrove just below Watlington. A sewage treatment works on the Pyrton Brook discharges into the Chalgove Brook. It is a small works and therefore does not have phosphorus removal on the effluent, resulting in high concentrations in the receiving water.
In 2015 the Environment Agency classified the Chalgrove Brook as “poor”, based on multiple factors including fish, macrophytes, and invertebrates (all of which are classified as “poor” individually). Water quality along the Chalgrove Brook is surprisingly classified as “high” for all measurable factors (under Water Framework Directive), except for phosphate which is “poor”. This is likely to be as a direct result of the sewage treatment works impact. The Chalgrove Brook was targeted to reach moderate status by 2015, which was successfully met, but on a cost-benefit analysis it is currently considered not feasible to improve the phosphate issue to more than “poor” status. We hope that this may change in the future as investment is put in to the sewage treatment works.
You can find out more about the classification of rivers in our catchment by using the Environment Agency’s Catchment Data Explorer.
We are hoping to set up Riverfly monitors along the length of the Chalgrove brook to monitor the effects of the sewage treatment works on freshwater invertebrates. To find out more about riverfly monitoring click here
Watlington Environment Group do great work looking after the Chalgrove Brook in Watlington, through their watercourses project. There is also growing enthusiasm in both Cuxham and Chalgrove to protect the stream particularly from encroaching development.
If you would like to get involved in joining or starting a local group in your area, then please get in touch.