For decades, experts have debated whether reducing the amount of nitrogen flowing into lakes can improve water quality in the long-term, even though blue-green algae can bind nitrogen from the air. However, no lakes with decreased nitrogen inputs have been monitored for long enough to clarify this – until now: scientists from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) have analysed long-term data to prove that decreasing nitrogen in Berlin’s Lake Müggelsee is the key to reducing algal blooms in summer. They showed that the amount of atmospheric nitrogen bound by blue-green algae is far too small to be used as an argument against the ecologically necessary reduction of nitrogen inputs.