The purpose of this paper is to analyse which navigational rights are applicable to foreign commercial vessels performing trans-arctic shipping through the Northwest Passage and how this affects the potential for Canada, through article 234 of the United Nations Convention on the Law of the Sea (UNCLOS), to issue national environmental legislation regulating pollution from ships. This is done through the method of legal dogmatics, characterised by analysis of the sources of law and the hierarchy between them. In this paper, the main sources of law employed are UNCLOS and relevant case law from the International Court of Justice. The main conclusions presented in the paper are that the Northwest Passage consists of a combination of territorial sea and exclusive economic zone, which generally means that commercial vessels are allowed innocent passage through the parts of the passage forming the territorial sea and are largely subject to freedom of navigation through those parts that form the exclusive economic zone. However, it seems likely that the Northwest Passage is a strait used for international navigation, in which case, the vessels passing through it are instead subject to the regime of transit passage. This would negatively affect the possibility for Canada to issue national legislation to regulate pollution from foreign vessels. However, as long as the Northwest Passage is covered by ice for most of the year, article 234 UNCLOS allows Canada far more leeway in regard to issuing anti-pollution legislation, both in the territorial sea and the exclusive economic zone, regardless of whether the Northwest Passage is found to be a strait used for international navigation. The passage regime applicable to foreign commercial vessels under article 234 could be characterised as a sui generis passage.