Essex Rivers Hub

This catchment includes the River Stour (split into 2 sections; Lower River Stour downstream of Lamarsh and Lower River Stour), River Box, Lavenham Brook, River Brett, Old River Brett and Bildeston Brook. Lavenham Brook flows into River Brett and the River Brett flows into Lower River Stour. Both Old River Brett and Bildeston Brook flow into the Lavenham Brook/River Brett area and the River Box is another tributary of the River Stour.

Phosphates are a catchment wide issue with all water bodies failing for this issue. The tributaries to the Stour have high levels with River Box, Lavenham Brook, Old River Brett and Bildeston Brook all having a WFD status of poor for phosphates whereas River Brett and the whole of the Lower Stour have the slightly improved status of moderate. More investigation is needed in this catchment to determine the sources of phosphate as it is unknown what the sources of this pollution are. Also in the River Brett there was deterioration from good to moderate so the reason for this deterioration also needs to be investigated.

Throughout the catchment the aquatic invertebrate populations are good and a great result for this area and an indication that water quality is generally good.

Dissolved oxygen is a failing element for 3 out of the 7 water bodies within this catchment. Lavenham Brook and Bildeston Brook have a dissolved oxygen classification of moderate and Old River Brett has a classification of poor. All these water bodies interact and flow into River Brett, which is not failing for dissolve oxygen, this river in fact have good levels of oxygen within the water. Therefore whatever is causing the failure is restricted to the upper reaches of the catchment. In most cases more investigation is needed to determine the cause of the low levels and for Old River Brett and Bildeston Brook, where the levels have dropped, the data needs to be looked at to determine if the failure is correct before investigating the cause. In Lavenham Brook the low levels have been determine to be due to natural factors such as low flows and higher temperatures in summer and early autumn. These factors also mean that any effluent entering the system has less dilution potential, which is also causing a lowering of dissolved oxygen. As it is not considered to have an adverse impact on this water body no action is needed.

Fish populations are a failing factor in 3 of the water bodies in this catchment; River Box, Old River Brett and Bildeston Brook. In River Box and Old River Brett the main impact has been identified as the barriers present in these water bodies, Old River Brett has a total of 20. These barriers will be expensive to remove and may perform an important function, therefore they need to be assessed to determine the best course to take to mitigate against this impact. Other factors identified are lack of good habitat and flow (old River Brett), competition between species for the available habitat, impacts from fisheries (River Box), maintenance of rivers damaging fish habitat (Bildeston Brook) and diffuse pollution. The other 4 water bodies within the catchment where found to have good populations of fish, in fact the Lower Stour improved from moderate to good status in 2009.

Diatoms are a failing factor for Lower Stour, River Brett, Old River Brett and Bildeston Brook. All of these water bodies are connected and flow into each other so it is possible that the failure has a common cause. The water bodies in the upper reaches of the catchment are classified as poor, while the Lower Stour, the river at the lowest point of the catchment, has a slightly improved classification of moderate. This suggests the impact on diatoms is heavier in the upper reaches. At this time the reason for the failures in all the water bodies is unknown and more investigation is needed to find the causes.

Macrophytes are only indicated as a failing factor in the Lower Stour but the reason for the failure is unknown and more investigation is needed.

Morphology or river structure is a problem within most of the water bodies within this catchment a part from Old River Brett and Bildeston Brook, in fact both these water bodies have been classified as good for morphology. For all the water bodies failing for morphology the WFD classification is moderate so only one classification away from good. This suggests that these water bodies are lacking some natural features and reduced in channel habitats. Many outstanding mitigation measures address some of these issues therefore they needed to be actioned to improve morphology overall.

Hydrology or flow is another issue that is resulting in a failure for many of the water bodies in this catchment and all those impacted have a WFD classification of moderate. Old River Brett and Lavenham Brook are not failing for flow and Lavenham Brook actually has a high classification for this element. In all cases the limited flows are not being considered a significant problem as in all cases the aquatic invertebrate populations are not being affected, therefore no action is planned at this time except to continue to monitor invertebrates to ensure there are no adverse changes. However failures in flow in some cases could be linked to the morphology failures so any work done to improve morphology may improve hydrology also.

Another issue of concern that may affect the water quality in this catchment is the list of pesticides and herbicides that are designated as being worked on under the Environment Agency's Safeguard Zone Action Plans. 

  • Metaldehyde - An organic pesticide used against gastropods in both household and agricultural settings. It is mildly toxic to other organisms, especially predators of gastropods (hedgehogs, frogs, wild birds), and may be linked to their recent decline. Read more.
  • Carbetamide and propyzamide - These are herbicides used in winter oilseed rape and winter bean fields which target various annual grasses and broad-leaved weeds. They pose no known risk to mammals, birds and bees but are highly toxic to aquatic organisms.
  • Nitrate - Comprised of oxygen and nitroten, this compound derives primarily from fertilisers and usually finds its way into groundwater and surface water via surface run-off. The UK and EU standards stipulate that the upper limit for contamination is 50 parts per million in drinking water and 50 parts per billion in fertilisers. Various water providers are working on plans to create modern nitrate removal plants to further the measures to protect drinking water. 
  • Clopyralid - A selective herbicide which internally disrupts various broad-leaved weeds, causing plant death. It is relatively persistent in soils but is generally of low toxicity to mammals, birds, aquatic organisms and other non-target organisms. 

Although there is evidence that the above chemicals pose a rather low risk to human health in low amounts, water providers continue to strive to abide with UK and EU regulations. 

 

The other 3 failing factors in this catchment are ammonia, annex 8 chemicals and outstanding mitigation measures. Bildeston Brook is the only water body failing for ammonia and annex 8 chemicals and both of these failures date back to 2009, before this both elements were classified as high. Therefore further investigation is needed to determine if the results are correct and if so what is the cause of these failures. In terms of ammonia throughout the catchment all other water bodies have low levels of ammonia. Many water bodies have outstanding mitigation measures that still need to be put in place. Firstly they need to be assessed to determine if they are still require andsecondly taken forward as soon as it is feasible. Lower Stour downstream of Lamarsh is the only water body with no mitigation measures listed so it needs to be determined if any are required.

The following mitigation measures are outstanding in this catchment:

  • Appropriate channel maintenance strategies and techniques – minimise disturbance to channel bed and margins.
  • Increase in-channel morphological diversity
  • Improve floodplain connectivity
  • Structures or other mechanisms in place and managed to enable fish to access waters upstream and downstream of the impounding work
  • Operational and structural changes to locks, sluices, weirs, beach control, etc.
  • Removal of hard bank reinforcement/ revetment or replacement with soft engineering solution.
  • Bank rehabilitation
  • Preserve and where possible enhance ecological value of marginal aquatic habitat, banks and riparian zone.

 

 

 

 

 

 

 

 

Website key stakeholders:

Environment Agency logo      Essex Wildlife Trust logo           

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