Loch Katrine is a freshwater loch and scenic attraction in the Trossachs area of the Scottish Highlands. It is within the district of Stirling. The loch is 13km long and 1km wide at the widest point and runs the length of Strath Gartney (Gaelic: Srath Ghartain). It is a popular destination for tourists and day visitors from Glasgow and nearby towns.
The loch derives its name from the term cateran from the Gaelic ceathairne, a collective word meaning cattle thief or possibly peasantry. Historically this referred to a band of fighting men of a clan; hence the term applied to marauders or cattle-lifters, the most notorious of whom was Rob Roy MacGregor who was born at Glengyle House at the northern end of the loch.
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.