In 1958, a study of the ecosystem in river Thames found it almost extinct. For more than 150 years it has been polluted by sewage dumping and residues from gasworks, until clean-up started in the 1960s. Last October, the Thames won the International Thiess River Prize for its environmental value. Thanks to efforts by the agency and water companies, water quality has improved so dramatically that the Thames now hosts more than a hundred different fish species, including salmon.
The phenomenon is being seen in a number of rivers across Britain, and not limited to fish. Plants, otters and water voles among others have reappeared in the environments they deserted decades before.
This particular study was based on the level of chemical pollutants present in the water, but river health can also be assessed is through its ecological quality: measuring the number of living organisms in the current environment, as opposed to a virtually clean one. European law (the Water Framework Directive) will soon make this measure the new benchmark.
The final step towards fully restoring wildlife in rivers like the Thames will be to help the development of a self-sustaining ecosystem and population.
Source: The Independent