The current study aims to investigate the mental models of primary school students about marine environments and how variables such as gender, grade level, and city of residence affect their mental models. To this end, 100 students were selected from each of the four grade levels of primary education in Turkey; thus, a total of 400 students participated in the study. In the analysis of the collected data, both statistical tests and the content analysis method were used. As a result of the analyses conducted, it was found that with increasing grade level, the number of the codes belonging to marine environments also increased significantly (X[superscript 2] (3, n = 400) = 151.296, p = 0.000). In other words, the students' mental models about marine environments were parallel to their grade level. In addition, the students' mental models about marine environments were not found to vary significantly depending on gender (U = 18,513, z = -0.861, p = 0.39 with effect size r = 0.04) and city of residence (U = 19,852, z = -0.129, p = 0.897, with effect size r = 0.006).