Positive and negative impacts of five Austrian gravel pit lakes on groundwater quality

► Groundwater fed gravel pit lakes might be in conflict with groundwater protection. ► Gravel pit lakes change biological, organic, and inorganic parameters of the groundwater. ► Gravel pit lakes might reduce nitrate, organic micropollutants, and hardness of the downgradient groundwater. ► Nitrate degradation rates were independent of the post excavation age. ► The anthropogenic post excavation usage has to be addressed critically.