Loch Katrine is a freshwater loch and scenic attraction in the Trossachs area of the Scottish Highlands. It is within the historic county and registration county of Perthshire and the district of Stirling. The loch is 13 kilometres long and 1 kilometre wide at the widest point and runs the length of Strath Gartney. It is a popular destination for tourists and day visitors from Glasgow and nearby towns.
It is the fictional setting of Sir Walter Scott's poem The Lady of the Lake and of the subsequent opera by Gioachino Rossini, La donna del lago.