But the campaign is more than just PR: every day, his team takes water samples and analyses them for the microplastic particles, tire fragments and drug residue. The pollutants decimate biodiversity in the Danube. In human beings, microplastics weaken the immune system and can even cross the blood-brain barrier. Andreas Fath refuses to accept this — also out of pure self-interest: he is an enthusiastic competitive athlete and would rather swim in clean waters. Carola Grau followed him on his journey from the source to the mouth of the Danube.