The goal of this study is to evaluate the comprehensibility of recently introduced water-sport prohibitive symbols by the Ministry of Knowledge Economy (MKE, now the Ministry of Trade, Industry and Energy) of South Korea, and to redesign the poorly comprehended symbols based on participants' feedback and three universal ergonomic principles. Evaluation of comprehensibility and cognitive features of fourteen water-sport prohibitive symbols were conducted with forty Korean participants. Only two out of fourteen symbols have comprehension rates higher than the level recommended by ISO standard. Four poorly comprehended symbols are redesigned based on ergonomic design principles and participants' feedback. A follow-up experiment with another group of twenty Korean participants was conducted to verify the effectiveness of the redesign process and results showed redesigned symbols have better adherence to ergonomic design principles and enhanced comprehensibility than the original ones. The findings may serve as a useful input for researchers and designers in creating easily comprehended symbols to promote safety. Relevance to industry: Warning symbols have long been used as an interface to communicate critical situation-specific information to prospective users in industrial undertakings so that the risk of accidents and injuries can be reduced. The findings of this study provide useful information for designers in developing easily comprehended symbols to promote safety.