Anecdotal and quantitative evidence of the Cougar's (Puma concolor) ability to swim across large bodies of water remains limited in the scientific literature. Here we report a 1.1-km swim by a dispersing male Cougar from the Olympic Peninsula to Squaxin Island in Puget Sound, Washington. We then predict the total number of islands in the Salish Sea that may be accessible to Cougars via swimming, using this Cougar's movement as a potential upper threshold distance, and present sightings records from islands in the Salish Sea to confirm or refute our results. We estimated that 3808 of 6153 islands in the Salish Sea could be accessible to Cougars with ≥1 or more 1.1-km swims, and we confirmed Cougar presence on 18 of those islands. Four islands with confirmed sightings required swims closer to 2 km. Increasing the threshold distance to 2 km yielded an additional 775 potentially accessible islands, including the 4 not captured by the 1.1-km threshold. Cougars are an umbrella species used to identify wildlife corridors across their range. We believe that improving our understanding of Cougar swimming abilities will aid us in determining the extent of habitat connectivity existing in the Pacific Northwest, where current habitat fragmentation characteristic of the Anthropocene may threaten Cougar metapopulation connectivity important to maintaining genetic health of the species.