River Chelmer

This catchment includes the whole of the Chelmer, Stebbing Brook, Boreham Brook and Sandon Brook. The Chelmer is 65km, Sandon Brook is 28km and Boreham Brook is 3km in length.



    Diffuse pollution




    Physical modification


    Fish passage


    Invasive species


    Point source

Click or tap a pressure to view the affected waterbodies

Click or tap a waterbody to view the pressures

The Chelmer is split into three sections; upstream of Great Easton, Great Easton to the River Can and the Lower Chelmer. The upstream section and the lower section have a Water Framework Directive (WFD) classification of poor while the middle section has a slightly better classification of moderate. The remainder of the water bodies are tributaries of the Chelmer and their WFD statuses are mixed. Stebbing Brook and Boreham Tributary has a classification of good so have reached good ecological status whereas Upper and Lower Sandon Brook have a moderate classification and Sandon Brook East has a classification of poor. Diatom (plants that are not visible to the naked eye) results start as poor (WFD status) in the upstream section of the Chelmer but have improved to moderate in the downstream section. Ammonia is classified as bad in the upstream section but has significantly improved to high in the middle and downstream sections; this suggests the source of the ammonia is in the upstream area. Fish populations are classified as good in the upstream and downstream section but within the middle section fish population classification has drop to moderate suggesting something is impacting on populations within this area. Phosphate levels are low in the upstream section and have a classification of good however within the middle and lower sections the classification has become poor. Therefore the sources of phosphate are concentrated from Great Easton and downstream of here. Dissolved oxygen is classified as poor in the middle section but this improves to high in the downstream section therefore investigations should concentrate in the middle section to determine the cause. Only the downstream section has data on macrophtyes (plants that are visible to the naked eye) which are classified as poor, annex 8 chemicals are classified as moderate and annex 10 chemicals are classified as a fail in this section, on the plus side aquatic invertebrates are classified as high. All three sections have good flow data.

Stebbing Brook flows into the middle section of the Chelmer and Boreham Tributary flows into the downstream section. Both these water bodies have good ecological status with good population of fish, high levels of dissolved oxygen and low levels of ammonia and phosphate.

Sandon Brook East flows into the Upper and Lower Sandon and the Lower Sandon enters the Chelmer in the downstream section. Fish populations are struggling in the upstream and east tributary of this brook but populations have reached good status within the downstream section. This may suggest that fish are unable to migrate past the downstream section or factors within the other parts of the brook are limiting fish numbers. Phosphate levels are classified as poor in the upstream section but have slightly improved to moderate in the downstream and east sections. This suggesting the phosphate inputs is higher in the upstream sections. Throughout Sandon Brook the results for dissolved oxygen and ammonia are good with high levels and low levels retrospectively. Diatoms are classified as poor in the east tributary but there is no data for the other two sections. All three sections have good flows.

Diatom failure is being caused by agricultural runoff, point source pollution and storm discharges in the upstream section of the Chelmer but the causes are unknown in the middle section of the Chelmer and Sandon Brook's East tributary. Further investigation is needed in all affected areas to determine reasons for failure or exact sources of pollution.

Ammonia is only causing a failure in one part of this catchment so data needs to be examined to determine if this failure is correct. If the results are correct then further investigation is needed to determine the cause of the failure.

Fish populations seem to be impacted by arable land use, field drains and flow abstraction in Upper Sandon Brook and barriers are also a likely impact in Upper Sandon Brook as well as Sandon Brook's East Tributary. Therefore in these areas farm visits are needed to discuss reducing impacts from this industry and fish passage needs to be look into. In the upstream section of the Chelmer, fish populations are also being impacted but the cause is not known, further investigation is needed here to determine the exact causes.

Phosphate failures are linked to agricultural land management, storm discharges, sewage discharges and road runoff. In these cases further investigation is needed to determine exact sources of pollution and to work with those causing these failures (landowners and water companies) to reduce their impact. In the Lower Sandon a water treatment emergency overflow was found to be the direct cause of the phosphate failure, therefore this needs to be tackled so that this source of phosphate is removed/reduced. The source of phosphate within the middle section of the Chelmer is unknown so further investigation is needed here.

The dissolved oxygen failure in the middle section of the Chelmer is linked to point source pollution impacts as well as natural seasonal variations of lower flows and higher temperatures in summer and early autumn. The low dissolved oxygen levels maybe impacting on fish populations in this section so further investigation is needed to determine if this is the case.

Annex 8 and annex 10 chemicals are causing a failure downstream of the Chelmer. The exact cause of the annex 8 chemicals is unknown; therefore further investigation is needed to determine if the results are accurate and if so what the cause of the failure is. The annex 10 chemicals are mainly entering the watercourse from the sewage treatment works (not directly from actions within the works but something that isn't currently removed from the waste water) therefore actions need to be determined how to tackle it at this source. Local action could be local environmental campaigns to reduce this pollution and raise awareness of the impact and determining effective treatments that can be carried out within the sewage treatment works to remove these chemicals. Another source is road runoff so SuDS schemes could be introduced to reduce the impact from this source.


Website key stakeholders:

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Design by LTD Design Consultants and build by Garganey Consulting based on an original concept by Herts and Middlesex Wildlife Trust