TO RIVERS AND WASTE SECTION
The trouble with water is that
it’s easy to dump things in it. Whether it’s sewage
or chemicals in rivers, bike frames in ponds, or oil and refuse
at sea, water is a convenient waste disposal system. We also expect
it to supply our needs, and we expect it to be clean. Other living
organisms expect the same, but they don’t have much say in
River bank with
Tyres dumped by
In fact water is very good at
recycling waste. It can cope with a great deal naturally, particularly
if the substances are reasonably ‘natural’ themselves.
Above a certain level, however,
or if the waste products are very toxic or chemically so complex
and '‘alien'’ that they do not break down easily, the
natural cleaning functions of water can no longer cope. The recycling
process itself breaks down. The result is pollution.
Leaves in stream
Humans don’t always cause
pollution. Leaves falling into a pond or stream and decaying can
cause pollution, but these effects are usually only local or temporary.
Sewage fungus in
Pollution from human activity
is much more significant and widespread. It may come from industrial
discharges, agricultural waste and fertilisers, roads, waste-tips,
and inadequately treated sewage from old or overloaded sewage works.