Loch Long is a body of water in Argyll and Bute, Scotland. The Sea Loch extends from the Firth of Clyde at its southwestern end. It measures approximately 20 miles (32 km) in length, with a width of between 1 and 2 miles (1.6 and 3.2 km). The loch also has an arm, Loch Goil, on its western side. Loch Long forms part of the coast of the Cowal peninsula and forms the entire western coastline of the Rosneath Peninsula. Loch Long was historically the boundary between Argyll and Dunbartonshire; however, in 1996 boundary redrawing meant that it moved wholly within the council area of Argyll and Bute.