Revival of northern Europe’s rivers offers lessons for
Northern Europe’s major rivers are coming back to life after centuries
of degradation and pollution. The leap of the salmon in some upper reaches is perhaps
the most visible sign of this.
Ambitious schemes launched in Europe in the 1990s to restore the habitat of rivers
and their surroundings have met with some success. And according to the authors of
a new FAO manual Rehabilitation of rivers for fish, new technologies and techniques
used in Europe have much to offer other countries, such as Argentina, China and Malaysia,
whose rivers and surrounding habitats are becoming increasingly degraded.
Rehabilitation schemes can also pay lofty dividends. In Europe, for example, restoring
rivers can help conserve threatened fish like the salmon and improve commercial fisheries
on inland waters that already produce some 170 000 tonnes each year. The growth of
recreational fishing can pull in more money while increasing profits of rapidly expanding
Reversing centuries of degradation
The revival of northern European rivers is long overdue. Here, as elsewhere in the
world, rivers have sustained an onslaught spanning centuries. Dating back to the
Roman Empire, people built dams, canals and aqueducts to provide drinking-water,
fill public baths and harness water power. And as forests were felled to clear land
for farming, increased silt runoff led to greater alluvial deposits and clogging
of clean gravel river bottoms.
The Industrial Revolution brought even greater destruction. In order to make it easier
to transport materials, river channels were straightened and deepened and vast canal
networks were constructed. This caused the eventual drainage of flood plains, destroying
habitat. Furthermore, increasing amounts of chemical and domestic wastes poured into
rivers, as towns and factories proliferated and grew. By the1950s, Europe’s great
rivers were all but dead.
So it was quite a day, in 1990, when the first salmon in 40 years was caught on the
River Sieg, a tributary of the Rhine that flows through North Rhine-Westphalia. “Many
water courses have gradually become much cleaner,” says FAO’s Gerd Marmulla. “Essentially,
this is why the fish are beginning to reappear.”
Many rivers have undergone a self-purifying process since the 1970s as more sewage
stations were built and old smokestack industries like steelworks and tanning factories
closed because of the radical restructuring of European industry. Cleaner technology
and better pollution monitoring have also played a part.
An example of a rerouted, channelized river compared
to its former pristine
status: its higher flow velocity, faster
drainage and lower habitat value increases stress for some fish populations
But that is only part of the story. Various river rehabilitation schemes have also
helped. On the Rhine itself, the Salmon 2000 project was launched after a warehouse
fire in 1986 caused a chemical spill into the river that killed thousands of fish.
The project is backed by the European Union and the countries through which the Rhine
and its tributaries flow - Germany, the Netherlands, Belgium, Luxembourg, Switzerland
and France. As part of the scheme, local authorities have been carrying out work,
for example, on the 153 km-long River Sieg to restore formerly indigenous salmonid
populations that had supported a strong fishery until the late nineteenth century.
Young salmon and sea trout have been released into the river and various obstacles,
including dams and weirs, have been removed or rebuilt to allow fish to swim to the
upper reaches where they spawn.
Supported financially by local anglers’ clubs, work has also been undertaken to improve
the habitat and water quality for the fish. Salmon need clean gravel beds for spawning.
So some potential spawning areas were cleaned in 1995 by scooping up the gravel and
allowing the fine sediment to be washed away by the current.
“We have seen an increase in the number of salmon reaching the Sieg,” says specialist
Marmulla, who has worked on the project. “There is every chance that we can build
a sustainable stock of fish that can increase even more over the coming years.” Full
recolonization, however, is a distant goal. Soil erosion in the catchment remains
a threat and can easily contaminate waters with agricultural chemicals.
But even here there are some hopeful signs. The European Union’s policy of setting
aside agricultural land is now encouraging landowners and local communities to restore
landscapes for uses other than farming. And on the Sieg, for example, legislation
has helped to create a diversity of habitats along the river banks. Further plans
exist to restore parts of the river channel to support fish and wildlife.
New design for fish passes: embedded-boulder
ramps allow easy passage of migrating fish, integrate well into the landscape and
are well accepted by migrating species.
“A key factor in this is that people’s thinking has changed,” says Marmulla. “They
are now more ecologically minded and this helps to keep pressure on the planners
and local authorities to increase efforts in favour of better environmental management.”
Lessons and choices
But there is much work to do and some European waters may never fully recover. Still,
there may be some lessons for developing countries, such as China and India, where
the damming of rivers has hit fish stocks.
Many developing countries are trying to come to grips with habitat degradation and
increasing pollution. India, for example, is tackling sewage pollution on the Ganges.
But the task is difficult and expensive for countries that must try to balance resources
and priorities, development and the environment.
“Developing countries should exercise careful environmental management while planning
for their energy and other vital development needs,” says Marmulla,“ as they often
still have the chance to avoid negative influences on their natural environments
and thus on the fish stocks that are an important source of protein for local people.”
Rehabilitation of rivers for fish, Oxford, UK, Blackwell Scientific Publications,
This new manual describes both the scientific theory and practical measures needed
to help rehabilitate rivers, their habitats and fish stocks.
Chemical obstruction may be caused by plugs of deoxygenated or polluted water, particularly
in the estuaries or lower reaches of rivers
Physical obstruction can be due to dams, weirs, rapids and waterfalls and may be
natural or artificial
River flow influences the willingness of migratory salmon to enter a river and move
7 April 1997