Evaporation is measured in practice with class „A” pans with tap water. The tap water composition differs from the natural water bodies. We wanted to make the water of our pans more like waterbirds to live water. We chose the seaweed because there was little research in this area and there are many seaweeds in the Keszthely basin. Data from our measurements were processed using Microsoft Excellel. Evaporation differences in each pan were compared to a two-sample t-test. We also monitored the development of the simplified water balance for the examined period. To count the mass change of installed plant material, the weight of seaweed was measured at the beginning and at the close of the experiment.