Site of Special Scientific Interest (SSSI) notified under Section 28 of the Wildlife and Countryside Act 1981.
Other Information
Part of the site is a Local Nature Reserve owned by Derbyshire County Council. Part of the site is managed by the Derbyshire Naturalists Trust as a nature reserve. Site boundary alteration (extension & reduction).
Description at Reasons for Notification
The site consists of approximately six miles of disused canal running from Cromford to Ambergate. It has been selected as an example of a eutrophic freshwater habitat with a rich submerged and emergent aquatic flora and a diverse marsh-wet grassland margin which supports a very rich insect fauna.
The canal is fed at Cromford by water from the Carboniferous Limestone but for the most of its length there are small feeders of more acidic water from the shales and gritstone. This variation in water chemistry has resulted in a range of plant communities. The canal is sufficiently shallow to be occupied to its full depth by rooted aquatic plants. The most widespread is broad-leaved pondweed Potamogeton natans.
Where there is sufficient light penetration rigid hornwort Ceratophyllum demersum and Canadian pondweed Elodea canadensis are locally abundant. Curled pondweed Potamogeton crispus is also present and apparently increasing with water starwort Callitriche ssp. occupying a more marginal position where the reedswamp communities are suppressed by shade from overhanging trees. Several rarer aquatic plants have been recorded including grass-wrack pondweed Potamogeton compressus, small pondweed Potamogeton berchtoldii, various-leaved pondweed Potamogeton gramineus, the rarer of the two hornworts Ceratophyllum submersum and round-leaved crowfoot Ranunculus omiophyllus.
Where silting has occurred, reedswamp communities are found right across the width of the canal dominated by reed sweet-grass Glyceria maxima or branched bur-reed Sparganium erectum. In this zone isolated clumps of water-plantain Alisma plantago-aquatica and the rarer Alisma lanceolatum, sweet flag Acorus calamus, and less frequently flowering rush Butomus umbellatus occur. Water forget-me-not Myosotis scorpioides and water mint Mentha aquatica are characteristic of this zone with water horsetail Equisetum fluviatile and the narrowleaved water-parsnip Berula erecta more local. Where the entry of side streams provides more nutrients, species such as unbranched bur-reed Sparganium emersum, great yellow-cress Rorippa amphibia, water mint and water-cress Nasturtium officinale are found.
On the upper banks and towpath margins the marsh grades into grassland. Here 190 herbaceous plant species have been recorded. This diversity is well structured and provides a continuity and variety of food niches for the important insect fauna.
Characteristic species are lady’s smock Cardamine pratensis, large bitter-cress Cardamine amara, meadowsweet Filipendula ulmaria, wild angelica Angelica sylvestris, hemp agrimony Eupatorium cannabinum and gipsywort Lycopus europaeus. Skullcap Scutellaria galericulata and marsh woundwort Stachys palustris are occasional, and the lesser spearwort Ranunculus flammula is local. A rare woodland plant found on the canal banks is the small teasel Dipsacus pilosus.
Thirty seven tree and shrub species are recorded within the canal boundaries. Alder Alnus glutinosa in many stretches forms a continuous fringe on the bank opposite the tow path. The boundary ‘hedges’ consist mainly of hazel Corylus avellana and hawthorn Crataegus monogyna with some wych-elm Ulmus glabra. Where broad margins exist between the tow path and canal boundary there are scrubby areas with hazel, elder Sambucus nigra and goat willow Salix caprea and occasionally guelder rose Viburnum opulus. For much of its length the canal has the character of a woodland ride, attracting insects from the woodland to feed on the canal flora.
A study of hoverflies Syrphidae has recorded nearly 80 species including a number of uncommon ones. Many are species whose larvae live in the reed swamp. Other groups of invertebrates have also been studied and confirm the value of this site.
The site is of local importance for grass snakes Natrix natrix and water shrews Neomys foetidens.