After the July 6th storms a high death rate was noted in the River Vesdre in Ensival, in the Verviers commune. The River Vesdre management allows for the possibility of fish in heatwaves, but also waste water discharged into the river.
The management says in a communiqué, “The River Vesdre is a river which was previously extremely polluted, mainly by the wool industry and population growth in Verviers. In recent decades the river has seen a dramatic recovery following purification of domestic waste water and industry linked, in particular, with the construction of a waste water collector in the 1970s. Also of assistance in this process was the bringing into service of water treatment plants such as Wegnez and Goffontaine, during the 1990s and 2000s.”
The management tool for water courses states that despite the improvement in water quality, certain black spots subsist, “Many houses situated by the river continue to send their waste water and certain sewers flow directly in the Vesdre, in the anticipation of connection to a treatment plant.”
The river management state these sewers were one of the main causes for the death of fish at the beginning of July. “During periods of drought, they do not correctly discharge waste water, with a lack of natural flushing, and consequently a large part of solid pollutants accumulate. In the first strong rain storm, these materials are carried and empty, in large volumes, into the rivers. There they decompose by consuming dissolved oxygen in the water. Such oxygen is necessary for aquatic fauna.”
The phenomenon is amplified when the flow level is low and the water temperature high. The management of the River Vesdre regrets, “The fish population, which battled for many years to recuperate in the Vesdre, disappeared over several kilometres. This was because the water quality was still insufficient, which was particularly evident in cases of water shortage.” However, it does hope that measures such as the removal of waste-water discharge, will be undertaken in a manner such that the mass killing of fish is not replicated.
The Brussels Times