The immediate reduction of plastic waste in the marine and coastal environment is deemed crucial in order to ensure and preserve environmental sustainability and ecosystem services for human well-being. Public information campaigns may contribute positively towards this direction, as they can have beneficial effects on increasing environmental knowledge, and thus, influencing citizens' environmental preferences and behavior. We attempt to examine the effectiveness of a public information campaign for the reduction of plastic waste, and specifically plastic bags, in the local marine and coastal environment of a major Greek island (Syros). A choice experiment was performed to evaluate individual preferences for reducing plastic waste pollution under different status of environmental awareness, prior and shortly after the information campaign, by means of a stated preferences method. The choice experiment was used to assess the values of several ecosystem services, likely to be affected by the accumulation of plastic litter in the coastal/marine environment, in order to incorporate all the related impacts that can be perceived by citizens and may influence their individual welfare. We selected four appropriate attributes that can be used to evaluate a public program which protects the marine and coastal environment of Syros from plastic waste pollution. Specifically: i) Recreational activities (e.g. bathing, water sports, sunbathing, etc.), ii) Landscape quality, iii) Biodiversity and iv) Commercial fishing activity. Subsequently, we formed a set of alternative policy options with different attribute levels (profiles) and paired these profiles to construct the "choice cards" (choice sets). Two surveys were conducted in Syros Island, administered by four trained interviewers, using face-to-face interviews by means of a structured questionnaire. The first one was conducted before the information campaign (first sample consisting of non-participants) and a total of 185 completed and useful questionnaires were collected. The second one was conducted during the campaign (second sample consisting of environmental campaign's participants) with 156 questionnaires being collected in total. The results indicate: (a) significant differences between the preferences of the two samples, (b) variations in the willingness to pay (WTP) values for the protection and preservation of the local marine/coastal environment between the two samples, though (c) there were not significant differences in their willingness to adopt new policy instruments (e.g. restrictions or bans of plastic bags). Τhe most important finding of our study is that the public information campaign significantly influenced the preferences of participants and was effective in terms of WTP, as the participants had a significantly higher WTP compared to the non-participants, assigning a higher economic value in terms of the overall (coastal/marine) ecosystem services affected by plastic waste.