The spread of anthropogenic litter is of concern for organisms being exposed to it. Most of anthropogenic litter consists of plastic, and several effects can occur from plastic exposure, such as entanglement and ingestion which fake a satiety and that results in slowly starving the mammals. Smaller plastic particles, such as microplastics (MPs), can affect mammals by entering the organs and possibly the cells with a damaging outcome. Since marine mammals prey on the same species as humans, that makes them a suitable indicator for predicting possible effects for humans. We analyzed the appearance of microplastic pollution in captive grey seals (Halichoerus grypus) in human care, by analyzing the contamination through water from the outdoor enclosure (inflow, the inside of the pool and outflow) and three species of fish (sprat (Sprattus sprattus), capelin (Mallotus villosus) and herring (Clupea harengus)), the seals are fed with. Fishes were examined for plastic pieces during fish sorting and before their gastrointestinal tracts (GI tracts) were re-moved for analyzing. Lastly, we analyzed feces defecated on the decks by one of the male grey seals. All three types of samples were analyzed for microplastics and the polymer type were determined by using Raman spectroscopy. Microplastics were found in the water (~250-370 fibers/pool and 40-45 fragments/pool), fish (~40-59 fibers/fish and 3-6 fragments/fish), and fecal samples (~60 fibers/feces and ~12 fragments/feces). Larger plastic pieces were observed among the fish before the GI tracts were removed, with the highest content found in October 2019. Particles analyzed using the Raman spectroscopy showed similarities to PVC, PS and PE.