Relation between the users of water in Bütgenbach and Robertville reservoirs (Belgium)

The salmonid Warche stream in eastern Belgium is fragmented by two dams and reservoirs (Bütgenbach in the upper reach, Robertville in the lower reach). This hydro-system is exploited intensively for different uses : production of hydroelectricity, production of drinking water, intensive tourism (bathing, sailing, fishing), reception of discharge of domestic and industrial effluents and flood control. The water quality is relatively good but there are two major problems : i) an eutrophication of the two reservoirs producing periodic blooms of blue-green algae, which pose problems for water treatment and cause toxic oxygen depletion and fish mortalities particularly in Salmonids; ii) a risk of bacterial contamination of bathing waters. The hydro-electricity production results in variations in the lake level that disturb the breeding success of certain fish species (pike and many cyprinids). Management of the different uses of water in the Warche basin and especially in the reservoirs, is complex and needs a multidisciplinary approach which takes into account the experience of similar situations elsewhere.