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be of paramount importance in ensuring the continuance of this
vital cycle of events. As some ⅔rds of London's water supplies
are extracted from the Thames, prevention of its contamination
can be seen in its true perspective.
Water, in its natural state, possesses the invaluable power of
self-purification but man's pollution of this essential commodity
reduces this unique property. Ecologically, growth of aquatic
plants and animals is not haphazard—it is determined by the
requirements of temperature, light, presence of chemicals and
concentration of dissolved gases, particularly of oxygen. Here,
then, is the raison d'etre for preventive measures in relation to
contamination of the River Thames.
Apprehension regarding pollution of the Thames is not new.
It was of some considerable concern to Sir Christopher Wren
when, after the Great Fire of London in 1666, he suggested that
his plans for the rebuilding of the metropolis should include
improvements to the sewage system.
During the 18th century salmon fishing was commonplace in
the River Thames but, with the introduction of the water closet
in 1810 and the necessity to use rainwater drains for the carriage
of sewage, the quality of the river water began to deteriorate.
Further exacerbation to the situation was occasioned by advancing
industrialisation and the growth of London as the centre of
an expanding British Empire. Together, these events resulted in
a rapidly increasing population so that by the mid-nineteenth
century the river was little more than a sewer.
In 1864, under the guidance of Sir Joseph Bazalgette their
Chief Engineer, the Metropolitan Board of Works completed
parallel intercepting sewers to the outfalls at Beckton and Crossness
and these arrangements still form the basis of London's present
sewerage system. Improvements over the last decade,
especially in the treatment afforded to sewage, has resulted in a
reversion of the river if not to its pristine quality then to something
approaching a state of wholesomeness not known for a
century and a half. The fact that fish are returning to the river
and its estuary gives ample proof of the improving nature of the
river water and the ability of the tidal Thames to sustain marine
life is such that, since 1967, some 55 species of fish have been
identified as inhabiting that stretch of water between Richmond
and Gravesend which 15 years ago supported none. However,
there is no room for complacency. Existing standards are only
to be maintained if problems of modern detergents, pesticides
and other chemical and metal contamination are surmounted and