Marine casualties, at sea or in port waters, are not only caused by large passenger or cargo vessels, which, due to their size, may have difficulty in giving way or stopping safely, but also small vessels such as marine yachts or jet skis, which have a high manoeuvrability but mistakes made when navigating or manoeuvring by the operators of these vessels can be serious. The aim of this article is to analyze the collision of two such crafts in port waters in the aspect of criminal liability of the perpetrator of the accident for causing it.