It is easy to dispose waste by dumping it into a river or lake. In large or
small amounts, dumped intentionally or accidentally, it may be carried away
by the current, but will never disappear. It will reappear downstream, sometimes
in changed form, or just diluted. Freshwater bodies have a great ability to break
down some waste materials, but not in the quantities discarded by today’s society.
This overload that results, called pollution, eventually puts the ecosystem out of
balance. Sometimes nature itself can produce these imbalances. In some cases,
the natural composition of the water makes it unfit for certain uses: e.g., water
flowing in the highly saline terrain of the prairies or gushing from highly mineralized
springs in some parts of the country cannot sustain fish populations.


But most often our waterways are being polluted by municipal, agricultural
and industrial wastes, including many toxic synthetic chemicals which cannot
be broken down at all by natural processes. Even in tiny amounts, some of
these substances can cause serious harm.

The Great Lakes, the Fraser River, and the St. Lawrence River are and
continue to be seriously contaminated by such toxic chemicals.

People dump hazardous materials into the ocean to get rid of them. Sewage
and waste from factories and cities can reach the ocean. This pollution is very
harmful. It can kill the plants and animals living in the ocean. Dangerous
chemicals like mercury kill the aquatic environment very quickly. Over 360
chemical compounds that have been identified in the Great Lakes. Many are
persistent toxic chemicals such as DDT, and mercury potentially dangerous to
humans and already destructive to the aquatic ecosystems.

For example, various species of fish now suffer from tumors and lesions, and
their reproductive capacities are decreasing. Populations of fish consuming
birds and mammals also seem to be on the decline. Of the ten most highly
valued species of fish in Lake Ontario, seven have now almost totally vanished.

How do you know when a river is polluted:

• If it has an uncontrolled amount of organic material such as sewage, milk,
  silage, liquids etc. that is affecting a waterway, the main sign that the water
  is polluted is that the water would be choked with vegetation.
• In the case of acid rain, the affect on the water is quite the opposite. The water
  will appear to be crystal clear. This is because the water is too acidic for fish etc.
  to live in.
• There may be bad smells where toxic waste is involved

Published in http://www.geocities.com/kamil_pollutionpage/WaterPollution.htm