STORAGE for: Freshwater ecosystems are characterised by complex mixtures of synthetic organic chemicals like pesticides, pharmaceuticals and personal care products, and industrial chemicals among others. These chemicals have the potential to jeopardise the ecological status of waterbodies. Gammarus pulex is a model species used in the field of ecotoxicology and many studies have been conducted using this macroinvertebrate to test apical and molecular changes led by chemical pollution. We collected Gammarus pulex from small streams characterised by these complex chemical pollutants in Southern Sweden and Central Germany as part of the FORMAS project MIXTOX (2020-00976). RNA was extracted and sequenced using Illumina Sequencing PE150. The aim of these medium project is to generate three de novo transcriptomes. One transcriptome will be representative of Swedish water systems, the second transcriptome of German systems, and the third will be a "core" transcriptome representative of both systems. All the mentioned objectives are part of the OB2 and OBJ3 in the FORMAS MIXTOX project. This storage project is linked to the medium compute NAISS 2023/5-308