Catchment area 6,867 ha, length 14.9km. Not designated artificial or heavily modified.


Waterbody description

The Swill Brook is spring fed from land to the north and west of Crudwell. It generally flows in an easterly direction through the parishes of Oaksey, Minety, Somerford Keynes, Ashton Keynes and Leigh before reaching the River Thames. The poor ecological status from 2010 to 2013 was probably due to natural low flows, signal crayfish and physical modification.

A river habitat survey was conducted in October 2013 (1) as part of the WILD project. The channel has been subject to extensive dredging in the past and low summer flows are exacerbated by the widened channel and embankments. The ecology is also constrained by over-shading on the banks which inhibits the natural regeneration to the original size. The extensive shading has encouraged the undercutting and slow destabilising of the southern bank in some areas in the Minety and Somerford Keynes parishes. The land either side of the brook is largely agricultural (semi improved sheep pasture and arable) with some angling and minerals businesses and holiday homes and the Wiltshire Wildlife Trust Nature Reserve/SAC that is Clattinger Farm. There is no significant buffer zone however it is protected from the livestock. Surrounding land regularly floods and although there is limited risk to villages or urban areas there are some individual houses and farms at high risk of flooding.



Species noted in autumn included species notes include Branched Bur-reed, Purple-loosestrife, Reed Sweet Grass, Reed Canary Grass, Jointed Rush Juncus articulates, Bulbous Rush, Yellow water-lily, Marsh Woundwort, Hemlock Water-dropwort, Pink Water Speedwell, Bogbean and Marsh pennywort.


Grass snake observed. Fish noted during low water levels included Dace, Minnow and odd Perch and Bullhead. There were signs of Otter along the entire river and Water Vole where shading was reduced.

Riparian habitat birds have been recorded (such as Kingfisher, Grey wagtail, Grey Heron, Mallard, Cetti's Warbler and Willow Warbler) and species more typical of pasture, hedgerows and woodland including, Wrens, Chiffchaffs, Song Thrush , Blackcap, Lesser Whitethroat Bullfinch Goldcrest, Robin, Dunnock, Blackbird, Song Thrush, Blue Tit, Great Tit, Long-tailed Tit, Chaffinch, Greenfinch, Goldfinch Sparrowhawk, Starling, Jackdaw, Carrion Crow, Magpie and Rook.


Main conclusions

Overall the Swill Brook through Oaksey, Ashton Keynes and Leigh parishes is of significant ecological value for its linear scrub & pond habitat, although the value of these habitats is limited by the severe low flows during the summer. The annual drying up of the channel means the river will only ever be suitable to species able to cope with the frequently dry conditions. This lack of water during the summer and early autumn means that the river is unlikely to reach good ecological status for fish for many years without significant restoration.

Oaksey (March 2016) Ashton Keynes Parish, March 2016. Leigh Parish (March 2016), Mintey Parish (February 2016), Somerford Keynes (January 2016)


Water Framework Directive

2016 Cycle 2 overall status now Moderate, including a Bad classification for Dissolved Oxygen (previously bad).


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