Natural England guidance

This site collection contains Natural England's conservation advice for this site. It fulfils Natural England’s responsibility under the Conservation of Habitats and Species Regulations 2017 (as amended), to give advice on how to further the conservation objectives for the site, identify the activities that are capable of affecting the qualifying features and the processes which they are dependent upon.

Natural England is in the process of updating Conservation Advice packages for all terrestrial sites. This is an ongoing process and the latest version will be available here on Designated Sites View.

Conservation Advice Components:

Additional information for consideration:

Background information and geography

Abberton Reservoir is a large storage reservoir owned by ESSEX and SUFFOLK WATER lying about four miles south of Colchester. It is the largest freshwater body in Essex and one of the most important reservoirs in Britain for wildfowl. It is outstandingly important as an autumn arrival point, moulting and wintering locality for wildfowl. About thirty thousand birds visit the reservoir annually including internationally important numbers of one species and nationally important numbers of twelve others. It is also one of a handful of sites in Britain where Cormorants nest inland in trees. The reservoir is less than five miles from the coast and many birds move between it and nearby intertidal areas and grazing marshes along the Colne and Blackwater estuaries.

The Reservoir was created between 1939 and 1941 by damming Layer Brook near its junction with the Roman River and flooding the long shallow valley to the south-west. In a wet or average year, most of the water pumped into Abberton is from the unsupported River Stour and in a dry year, the River Stour is supported by flows from the Ely Ouse to Essex Transfer System.. Two causeways divide the reservoir into three sections: west, central and east. The eastern section is by far the largest and was constructed with concrete banks, unlike the other two sections. At the time of classification the reservoir's standing open water covered about 471 hectares. An additional 247 hectares of adjacent wetland, grassland, woodland and arable were included within the SPA as supporting habitat.

Between 2010 and 2014, ESSEX & SUFFOLK WATER undertook major construction works to enable water levels in the east section to be raised. The top water level was raised by 3.2 metres and the reservoir was completely filled by April 2015. Levels have not been raised in the other two sections (which receive water from Layer Brook but not from the Stour) and water is now pumped between the central and east sections. As part of the level raising scheme, the east section's concrete banks were removed and its shoreline re-profiled to create large areas of shallow wetland habitat for the site's waterfowl. Before the main construction period, new lagoons were also created around the west section to provide more habitat for wildfowl in a part of the site well away from the main works. Detailed bird monitoring showed no declines in bird numbers at a whole-site level as a result of disturbance during construction. But the way species use and are distributed within the site has changed, particularly because the east section now has extensive shallow-water habitat, and water levels in the central and east sections can be controlled independently.

As a result of the level raising scheme, the reservoir now covers about 670 ha at maximum extent, an increase in area of about 40% (ESSEX & SUFFOLK WATER 2015). The western section of the reservoir is 16 ha (excluding the scrapes created in 2001 and 2004). The central section of the reservoir is 49 ha in extent. The raised eastern reservoir section was designed to have an extent of 604 ha. Due to the enhancement scheme, when the current reservoir is 65% full, it is the equivalent of the old reservoir at 100% full. Since enhancement, several bunded bays and lagoons create shallow water habitat and exposed areas.

As part of its operation at Abberton Reservoir, ESSEX & SUFFOLK WATER carries out a process of draw down and re-filling. The process involves beginning re-filling the reservoir in November with the aim for it to be full by the end of April. Then the draw down starts in July leading back to re-filling beginning in November. The reservoir has been designed so that it can be drawn down as low as 25% and will still provide increased and sufficient habitat for the designated waterfowl species. However, the reservoir normally operates between 50% and 100% full (Essex and Sussex Water pers. comms, 2019). This means that during the important overwintering period the reservoir is gaining water while during the autumnal passage period the lower water levels allow the appearance of an island within the reservoir which supports possible moulting waterbirds. The draw down and refilling process primarily affects the eastern section. The water level in the western section is managed by a weir so there is very little fluctuation in the area of surface water. It was originally agreed that the central section would be managed in a similar way to the historical draw down and re-fill pattern. However, recently it was agreed that keeping the central section more stable with a smaller draw down would be more beneficial, and so it is unlikely that this section would see substantially changes in water levels.

Parts of the east section now lie outside the SPA boundary and some of the original terrestrial habitat within the SPA has been lost. However, there is sufficient land in the water company's ownership around the new shoreline to make up for these losses and large areas of new shallow-water habitat and semi-natural margin have been created.

Site maps

Use the MAGIC website to see site maps, including habitats, species and other marine designations.

These maps are based on best available evidence, there are some caveats associated with the maps on MAGIC.

Further information

For further information relating to this designated site you can refer to the following resources:

• EU Habitats Directive and EU Birds Directives reports from JNCC
• Natural England's SSSI information, including condition assessment
• the RSPB bird guide
• Wetland Bird Survey Alerts from BTO
• Images are used under creative commons license

Other information:

• Joint Nature Conservation Committee provides advice on habitats and biodiversity
• Site Improvement Plans were developed during the Improving Programme for England’s Natura 2000 sites (IPENS)

For further information about this site contact:

• Natural England enquiries Telephone: 0300 060 3900. Email: enquiries@naturalengland.org.uk