The presence of (micro-) plastics in marine systems has been investigated in a multitude of studies over the past decades. Yet, the contamination of freshwater systems has just recently caught the attention of scientists. This lead to an increased insight of how quantitatively and qualitatively (micro-) plastic has contaminated freshwater systems in sediments and the pelagic zone. Due to its high abundance (micro-) plastic has become available to a multitude of organisms, spanning over a broad band of trophic levels, which might lead to the accumulation of (micro-) plastics within the food web. The uptake of microplastics has been proven for a multitude of species, also including the freshwater crustacean Daphnia, which inhibits a central role in the limnic food web. Up till now, the effects of microplastic particles on freshwater organisms are poorly understood as the research is in it's infancy. Goal of this thesis is to investigate the possible effects of microplastics and associated additives on the morphological and molecular level of different Daphnia species.