(b) Reservoirs
The very large reservoirs used for water-supply are of value to dragonflies as potential
'hunting' grounds, especially where suitable breeding sites exist nearby, but most are
relatively unsuitable as breeding sites. This is because they usually have hard, artificial
banks which inhibit the growth of the marginal and emergent vegetation which is so
important for many species to complete their life-cycle. Nevertheless, even in the
absence of such vegetation, some species, such as Enallagma cyathigerum (the Common
Blue Damselfly) may swarm in enormous numbers at some reservoir sites. Essex has a
number of very large reservoirs. These include the Walthamstow group in the far west of
the county. Hanningfield in south-central Essex and Abberton and Ardleigh in the
north-east. Where sheltered enclaves with a reasonably well-developed marginal
vegetation exist, as many as nine species have been recorded.
(c) Lakes
There are no natural lakes in Essex. Apart from reservoirs, the remaining large areas
of still-water habitat in Essex are mainly a by-product of mineral extraction, or have
been created deliberately as lakes for their ornamental or recreational value. From the
18th century onwards it was fashionable to form artificial lakes - usually by damming a
stream - in the parkland surrounding the grander country houses. Many of these have
survived, and some, such as those at Hatfield Forest and South Weald Park, are now
open to be enjoyed by the general public. Private land-owners continue to create such
lakes for their ornamental value, or for fishing, wildfowl or water-sports, and public
authorities, too. increasingly include lakes for their landscape or amenity value when
designing open-space amenity areas. Two examples are the recently formed lake at
High Woods. Colchester, and the small lake in the grounds of the new General
Hospital, also at Colchester. Newly formed lakes are quickly colonised by such species
as Enallagma cyathigerum (the Common Blue Damselfly) and Orthetrum cancellatum
(the Black-tailed Skimmer). Where the surrounding terrestrial environment is
adequate, and aquatic vegetation is allowed to develop, other species follow on. Some
fifteen species have been recorded as breeding in this type of habitat in Essex, although
one of these. Calopteryx splendens (the Banded Demoiselle), does so very rarely. Well-
established ornamental lakes are important as breeding sites for one species.
Erythromma najas (the Red-eyed Damselfly). which is very local in Essex, and they arc-
also very important as dragonfly 'oases' in otherwise heavily built-up areas (the
Wanstead Park lakes are a good example of this).
The persistence of a rich dragonfly fauna at such sites as these is threatened by over-
enthusiastic and tidy-minded management which restricts the growth of marginal
vegetation, or converts surrounding terrestrial habitat to the formal short-grass regime
of many of our urban parks. A depressing example of this is (he above-mentioned lake
at High Woods. Colchester, though there are some recent signs of improvement here. A
further step in this process is the creation of artificial banks by means of vertical wooden
piles, or concrete slabs. This is sometimes defended as a means of offsetting erosion
caused by too much trampling of the waterside, and there is no doubt that this is a
problem in some of the more popular locations. The almost completely denuded and
sterile margins of the ponds at Leyton and Wanstead Hals are unfortunate examples of
excessive erosion. Even here, though, a preferable strategy would be to selectively
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