When a polluting source is established to be a historic wreck the obligation of States to preserve the marine environment could contradict their duty to protect submerged objects of an archaeological and historical nature. This thesis will aim to examine the international conventions that govern the protection of underwater cultural heritage and the removal of potentially polluting and hazardous wrecks. It will endeavour to identify which norm would take precedence in a situation where a State has both the obligation to protect the marine environment and a duty to protect underwater cultural heritage. It will analyse State practice when faced with such a situation in order to identify the possibility of the emergence of a new rule of customary international law requiring States faced with an environmental threat from a wreck that is of historical or archaeological importance to eliminate the threat whilst at the same time protect and preserve the wreck in situ with minimal interference. Therefore, the examination will be centred on the question of the extent to which the application of the Nairobi Convention could be in conflict with the application of the UNESCO Convention, with the view of clarifying the legal grounds upon which a State can interfere with a historic wreck that is hazardous. To this end, this research will identify the significance of the two conventions and why their creation was unavoidably determined by prior circumstances. It will provide an examination of the two conventions as well as an analysis of the relevant provisions of UNCLOS being the foundation of the international law of the sea. The examination will delve into and highlight possible conflicts that may arise between the conventions. Finally, the premise of this thesis, is to present the possible emergence of a new rule of customary international law. In doing so, the thesis contributes towards the clarification and further development of customary international law.