Beach safety flags form an internationally adopted warning system intended to prevent adverse incidents, including drownings. However, little is known about people's familiarity with these flags. In this study we tested the recognition and understanding of beach warning flags in the Netherlands, a country which welcomes millions of beach visitors every year. A convenience sample (N = 174) of the Dutch population was interviewed using a structured survey which asked for the meaning of eight different flags, the respondents’ confidence in their choice, as well as their intention with regard to entering the water. The results show an overall poor understanding of the meaning of all flags except for the red flags (which indicate high hazard). The level of confidence largely followed the same pattern, with low confidence for most flags except the red ones. Strikingly, the yellow flag (which indicates potential hazard and is meant to discourage bathing) evoked a considerable proportion of opposite associations (i.e., safety), combined with moderately high confidence and intentions to enter the water. More people were in fact inclined to enter the water under a yellow flag than under a red & yellow flag (which indicates a patrolled beach). Direct or indirect experience with danger in the sea did not affect people's knowledge of the flags but did reduce the intention to enter the water. We conclude that familiarity with the flag system in the Netherlands is wanting and we propose a number of recommendations to improve public understanding.