Among the factors that make a settlement of the water for the larvae of the blue-wing demoiselle impossible to include on the one hand, the channeling and obstruction of the same, go where the lost for the settlement of important aquatic plants. On the other hand, the eutrophication of water by agriculture and by household wastewater causes an important factor in the decline dar. this to increased sludge formation and therefore increased oxygen consumption in the affected waters and to increased algal growth of so-called " slime algae ". It is brown and green algae, the water plant and the substrate is overgrown. The veralgten plants are not accepted by the females as oviposition sites. In addition, the larvae no holding facilities are against the current, and the algae and dirt particles settle to the gill lamellae are important for respiration. The algae is followed by weeds and ultimately a silting of water bodies.