Cnidaria stings cause a wide range of cutaneous and systemic symptoms, normally occurring shortly after the venomous insult (1). We report a case of worsening cutaneous reaction over an eight-year period following a Cnidaria attack sustained whilst maritime swimming. The lesion was characterised by severe, ulcerating chronic inflammation that required wide local excision and skin grafting. Prevention and early identification of Cnidaria envenomation is important for those treating maritime swimmers.