In its 2021 annual report, the World Health Organization (WHO) presented data which estimated that 236 000 people died from drowning worldwide in 2019. Furthermore, the data indicates that drowning is among the top five causes of death in children under the age of 15, typically in preschool and school children. Swimming skills enable young people to participate in various water-related activities. If a person is not a swimmer, they will often be excluded from such activities or they will be quiet about their non swimmer status, thereby edangering themselves or others. The research was conducted on a sample of 353 fifth-grade students in 25 elementary schools in Osijek-Baranja County in order to examine the self-assessment of swimming knowledge. Students filled out a questionnaire, in which they answered positively or negatively about their swimming skills. Along with the questionnaire, the swimming knowledge criteria was attached in detail so that students had a clear picture of the required level of knowledge. Students who considered themselves to be swimmers were tested in a deep pool in order to examine the level of swimming skills. The initial subjective assessment of swimming skills was attended by 684 fifth-grade students of primary schools in Osijek-Baranja County, except of those in the city of Osijek. Out of 684 students, 331 (48%) declared themselves non-swimmers, while 353 declared themselves swimmers (52%). Therefore, 353 students took the swimming test. After that test, it was established that 261 students have the necessary swimming knowledge, which is 38.1% of the total number of students. The test revealed that 92 students who considered themselves swimmers do not have the necessary swimming knowledge, which is 13.5% of the total number of students. Statistical analysis was performed using the t-test. A p value of 0.000361852 was obtained, which showed that there is a significant statistical difference in self-assessment of swimming knowledge and actual swimming knowledge.