ANIMAL LIFE OF ESSEX RIVERS AND SEWAGE WORKS 147
identical place and until September of that year she was always
available when we wanted her. Unfortunately we have not seen
her since to check if she again hibernated in the same place.
References
Wheeler, A. C. & Malenoir, G. (1959). A first report on the reptiles and
amphibians in Epping Forest (1958-59). Essex Nat, 30: 179-188.
Malenoir, G. Albinos in Essex (1960). Essex Nat., 30: 280.
Notes on the Effect of the Severe Winter 1962-63
on the Animal Life of Essex Rivers and Sewage
Disposal Works
By A. W. Davies
The average thickness of ice on rivers of any consequence, for
example the rivers Stour, Colne, Blackwater, Chelmer and Crouch,
above the tidal limit was about 5"-6". This resulted in the estab-
lishment of low dissolved oxygen levels in the river water which
led to the death of some fish. However the effect of this oxygen
depletion was not as severe as with standing water.
For ponds with a total area of 1/2 acre or less, the ice often
extended to the bed, resulting in the death of very large numbers
of fish. They probably died because of the establishment of
anaerobic conditions below the ice and became frozen into it later.
Only when the ice began to melt was the full extent of the fish
destruction appreciated. A few examples are given to illustrate
the extent to which fish deaths occurred.
In North Ockendon ponds some 2,000 fish died including
Roach, Perch, Crucian Carp and Rudd. At Mardyke Farm pits
some 200 fish died, mainly Carp and Rudd, while at Valence Park
Lake over 300 fish, mostly Roach 4"-6" in length, were found to
have died, some 1,000 having already been removed and buried.
At Eastwood Rise pits 800 fish including Roach, Rudd, Carp and
Perch died. This is a very sinister picture which could be extended
to almost all ponds and lakes in Essex and indeed throughout the
country.
Sewage works often attracted some very strange visitors. For
example, Ingatestone Sewage Disposal Works had many hundreds
of Moorhens feeding on the sludge of the sludge drying beds. At
Witham the polishing lagoon for sewage effluent was frequented
by large numbers of Coots, Grebes and Mallards, the latter also
being found on the irrigation plots of a number of sewage disposal
works. Of the birds which normally frequent the percolating
filters of sewage works, Wagtails and Starlings showed a striking
increase in numbers; other birds not normally found on these
filters, Blackbirds and Blue-tits, were also found in abundance.