Even though the ocean is a defining feature on Earth that regulates climate and provides oxygen, food, and jobs, students still have low to moderate marine and ocean literacy knowledge. Ocean literacy is an understanding of the ocean's influence on people and people's influence on the ocean. It is an emerging need necessary for ensuring the sustainability of the ocean and its resources. The UN ... [Show full abstract] has declared a Decade of Ocean Science for Sustainable Development, and one of the priority research and development areas is ocean literacy. Unfortunately, marine science and ocean literacy topics are poorly represented in school curricula across the world. This study presents the level of marine knowledge in a sample of primary school students before and after different themed non-formal educational interventions and the effect of non-formal educational activities on students' knowledge. These activities led to significant increase in the knowledge level three weeks after they were performed, indicating the retention of gained information. Performed educational activities and knowledge transfer from graduate level to primary school level significantly increased the level of students' knowledge, and consequently ocean literacy, and revealed some of the learning misconceptions. Results of this study show that there is a need for an integrated approach to the teaching of Ocean Literacy starting from the early grades by combining teacher's professional development, strengthening ocean-related topics in school curricula, and promoting non-formal educational activities.