A habitat for specialist flora associated with magnesian limestone.

An Ecological Assessment of


The underlying geology of Castle Lake is solid, Permian magnesian limestone. Soil types are predominantly light, magnesian limestone and till. Castle Lake, as a water body on limestone, is a comparatively rare habitat. As Durkin has underlined with regard to magnesian limestone habitat, ‘the porous nature of the limestone reduces the likelihood of ponds and marshes forming on its surface. Only the presence of glacial boulder clay here and there creates a waterproof liner for wetlands.

Consequently, ponds are very scarce on the limestone, and most are in old clay pits. They often have a richer flora than ponds on the coal measures. Particularly important are “flushes”, which are grasslands on sloping banks, with calcareous water trickling downhill’ (Durham Wildlife Trust, 2007).

The north of the lake is shallow with peat formation. Lowland peat bog is a rare and increasingly threatened habitat. The shallow basin formed by Castle Field and quarrying activity allied to poor water drainage provided ideal conditions for peat formation, as plant decay is slowed leading to layers of decomposing plant material. In addition, this boggy habitat may also have been supplemented by humus sediment from a sewage works that previously operated in this area from the early twentieth-century (now superseded by the current works).

A surviving small ruined brick building in situ may be a remnant of this plant. The shallow character of the north end of the lake allows extensive bare mud areas to develop in the autumn. This provides a rich feeding area and is especially attractive to feeding birds, although constant grazing has denuded this boggy area of flora of importance. The central section of the lake is deepest with a maximum depth of 1.5m. To the south, the lake is more of a gravel substrate with recently a planted Phragmites reed bed on the western edge. Areas of fencing have been erected to remove grazing pressure to develop marginal vegetation.

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Flora & Fauna @ Castle Lake
Eco Assessment Report

Tree cover around the lake is minimal, with sporadic Crack Willow (Salix fragilis) shrubs only of note.

The boundary hedges of the surrounding fields predominantly consist of Hawthorn (Crataegus monogyna), Dog Rose (Rosa canina) and Bramble (Rubus fruticosus), with also occasional Oak (Quercus robur), Ash (Fraxinus excelsior), and Sycamore (Acer pseudoplatanus). Notably, many of the hedge-lines are shown on the Ordinance Survey map of 1888, thus indicating their longevity, and also that possibly of some of their tree-species, indeed the Foumarts Lane access route and field boundaries is lined by numerous mature trees, including Beech (Fagus sylvatica) and, notably several Hornbeam (Carpinus betulus), a relatively scarce species in Northern England.

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A comprehensive inventory semi-natural grasslands carried out during the summer of 2006 (Stobbs & Durkin, 2007) of the Sedgefield area included several sites around Bishop Middleham, including Bishop Middleham Castle Field. This was identified as a particularly rich grassland habitat that supported a wide range of significant flora.

The field is particularly noteworthy as ‘it consists of dry and generally calcareous grassland with the better flora coinciding with areas of stone originating from the Castle foundations there are some steep gradients within the field which, together with the grazing regime, have helped to keep the grassland generally short’. Recommended management of Castle Field suggested that the current grazing regime was ‘satisfactory’ and that there should be no variation to this.

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Damselflies and Dragonflies:
Common Blue (Enallagma cyathigerum)
Large Red Damselfly (Pyrrhosoma nymphula)
Blue-tailed Damselfly (Ischnura elegans)
Common Sympetrum (Sympetrum striolatum)
Common Aeshna (Aeshna juncea).
Four-spotted Chaser (Libellula quadrimaculata)
Common Darter (Sympetrum striolatum)
Given the wet habitat of Castle Lake and the availability of multiple shallow pools, it is noted there is definitely under recording of species of damselflies and dragonflies.

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Smooth Newt (Triturus vulgaris)
Common Frog (Rana temporaria)
Common Toad (Bufo bufo).

Mammals are under-recorded at Castle Lake: for example, notable by their absence are any formal records of any species of mouse, vole or shrew, which, given the habitat and regular sightings of birds of prey and owls, are undoubtedly present in some numbers.

It is highly likely that Otter (Lutra lutra) is also present, given the size of water body, availability of food, and the nearby Still drain and River Skerne watercourses. Water Vole is probably the most significant mammal species recorded, with individuals noted in the lake and also the River Skerne. The population of Water Voles has undergone rapid decline, due to habitat destruction, the intensification of agriculture, water pollution and the spread of the introduced American Mink (Neovison vison).

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Fantastic range of Mammals


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If you visit the site please record the species of birds you see along with any interesting flore or fauna. Please send the information info@castlelakecg.co.uk