Platycnemis pennipes is essentially a mediterranean species, with a decidedly southern
distribution (i.e. south of the Wash) in Britain. It is also intolerant of even slight
pollution. Its remaining sites in Essex are in moderate to slow-moving reaches of three
river-systems only. These are: the River Lee/Cornmill stream; the Roding; and the
Chelmer/Blackwater. In the Lee Valley it is abundant at several sites, being probably the
most common species at one of these. On the Roding it is also common at a number of
places, and is probably more widely distributed along the River than its distribution-
map suggests. Along the Chelmer/Blackwater Navigation it is thinly distributed in what
appears to be declining numbers, but a strong colony has recently been discovered in an
E.N.T. reserve on the Sandon brook, a tributary of the Chelmer. All of its Essex sites are
richly vegetated rivers and streams, mostly with adjacent flood-meadows, though one of
its strongholds (the Roding) runs through intensively farmed arable land. Its habitat on
the Chelmer/Blackwater still seems visually suitable for the species, so that its decline
there may be due to water pollution (either from river-traffic or agricultural run-off).
This species is nationally vulnerable, due to pollution and insensitive river-
management, and the Essex colonies appear to be the last remaining ones in the whole
of East Anglia. The conservation of Essex sites for P. pennipes is therefore of significance
even in the national context. It appears to have already been lost from the Stour, and
could soon disappear from the Chelmer/Blackwater. Dredging proposals on the River
Lee/Cornmill Stream complex constitute a further major threat to it. at its most
important Essex locality.
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