Aquatic environment pollution

What is pollution ?


Pollution is a complex concept that can be perhaps defined as an overabundance (beyond a threshold or a norm or law) of an element in an environmental compartment where it is naturally absent or present in lower quantities and whose presence hinder the good equilibrium of the environment. In the Walloon region, watercourses and wetlands are still too often the object of diverse pollution events. Despite the awakening environmental conscience and the efforts undertaken to improve the quality of our aquatic environments, several years of actions can be jeopardized in a few minutes.


Aquatic environment pollution



«The Sambre is polluted», «The Légère Eau brook is an open sky sewer …», «Dead fish», «Urgency plan for the Dendre», «Hydrocarbon pollution»… These titles taken from several regional dailies are unequivocal: our watercourses are still too often the object of pollution.



October 6th 2006 - Now pollution on the Dendre in Ath


A new pollution coming from the western Dendre has reached the Dendre in the morning of this Friday, October 6th. The fish and the ecosystem of the watercourse are again, victims of recurrent pollution. The activities of the sugar plant of Brugelette are under the spotlight but the first analyses may deny this hypothesis. So as to try to save what can still be saved, emulsifiers have been placed on the Dendre at the Maffle lock and the firemen have ventilated the water after the Rebaix and Papignies locks.

Consult information on other pollution events…>


The defence and restoration of water quality in our watercourses are part of the mission of the Maison wallonne de la pêche. Our determination in defending the aquatic environments has already leads us to have a civil role in several pollution events:



The different types of pollution

Organic pollution

Organic matter is naturally present in a river. It is decomposed by bacteria that during the process consume oxygen. Important introductions of organic matter cause the explosion of the number of these organisms. The available oxygen is used in the decomposition process and the fauna will not have enough left.


Mineral pollution

Mineral salts are compounds absorbed by the plants to ensure their growth and their development. Certain elements, present in low quantities in a balanced natural environment (N and P), limit the vegetation growth. The presence in important quantities of these elements creates the conditions for the eutrophication of the water body: the proliferation of aquatic vegetation.


Thermal pollution

The origin of thermal pollution is essentially the industries (thermal centrals, metallurgic…) that use water in their cooling circuits. The water is the rejected, bringing about the warming or the river water and diminishing the concentration of dissolved oxygen. The fauna of our watercourses withstands poorly these drastic modifications of their environment.


Chemical pollution

The pollution is caused by chemical products (hydrocarbons, heavy metals, detergents, herbicides...) having varied events: creation of a film on the surface of the water reducing the exchanges between water and air, perturbations in the biological mechanisms and equilibriums, disruption of fish hormonal systems…


Physical pollution

Physical pollution concerns all the floating objects we find in the bed of a watercourse but also the clandestine depositions made on the banks: construction materials, garden waste, kitchen scraps... These deposits can enter the watercourse where they will fill up the riverbed and induce organic pollution.



Pollution sources


Domestic origin

Water is indispensable: in Belgium an inhabitant uses around 180 L of water per day, for drinking, personal hygiene, cleaning… The various uses of water are pollution sources. In the absence of depuration, the wastewaters are rejected directly on the watercourses and cause the degradation of the river environment.


Agricultural or forest origin

Agriculture uses and produces substances that are potentially pollutant. The manure and herbicides used in agriculture can be carried by surface draining and affect the watercourses. Farm effluents can also contaminate the environment by surface draining or percolation.


At the forest level, certain practices give rise to pollution. Planting resinous trees in the banks leads to an accumulation of needles in the riverbed and an acidification of water, the abandoning of residues on the banks and the passage of exploitation machines through the riverbed are some examples.


Industrial origin

In the course of their activities the industrials some times use the water of our watercourses. Despite the legislation and the controls, the quality of water is changed and upon its rejection it causes toxic and/or thermal pollution in our watercourses.



Measuring pollution

Different parameters allow regularly evaluate water quality: suspended matter, organic load (BOD5 and COD), nitrogen load (N) and phosphorous load (P)...


There are indexes that allow also to evaluate the biological quality of a watercourse and to measure the cumulative effects of pollution: IBGN, IBIP, and IPS...



Avoiding pollution

It is often easy to lessen the impact of man on the quality of our watercourses through daily actions. There are two types of actions: the preventive actions (limit the quantity of waste…) and curative actions (build water treatment plants, limit the entries of manure from agriculture, conserver and replant hedgerows…)

Voir aussi :

→ Podcast saumon atlantique
→ Les poissons de nos rivières
→ Les frayères artificielles
→ Stages de pêche
→ La pêche au féminin