Marine litter is recognized as one of major threats for the marine environment. The international legislative framework requires the evaluation of the amounts, trends, and potential threats of marine litter on the biota. Similarly, for Habitats Directive listed species there is a need to report on pressures and threats to assess their conservation status. Through repeated sampling of floating macro-litter and cetacean species along a fixed transect between Spain and Italy, this study provided three years worth of detailed data in the SCI of the Bonifacio Bouches, the narrow sea passage between Corsica and Sardinia. The area includes a variety of marine habitats of high ecological richness, hosting marine species listed in Annex II, like the bottlenose dolphin that is regularly present. However, the area is affected by heavy human pressures linked to shipping lanes, recreational activities, tourism, that represent sources of marine litter. Showing evidence of the potential impacts of litter on the biota is important to promote cooperation and networking between scientists, policy makers and citizens, in order to favour sustainable development and combined management measures. In marine protected areas this information is used as a tool for good management at the local scale, but needs to be included in a wider vision in order to create a network among the different initiatives. Our results showed that there is a high density of plastics in the Strait all year round, with large amounts accumulating in certain areas in spring/summer, due to a combination of multiple factors. This can be particularly detrimental for the local dolphin population, often sighted within these accumulation areas. The potential for interaction now needs to be verified at a finer scale through the promotion of local monitoring programs, involving adjacent MPAs in networking collaborations.