Loch Katrine is a freshwater loch in the district of Stirling, Scotland. It is roughly 13 kilometres long by 1 kilometre wide.

Loch Katrine is the primary water reservoir for much of the city of Glasgow and its surrounding areas.

The lake of Sir Walter Scott's The Lady of the Lake is Loch Katrine.

Oil-fired vessels are not permitted to sail its waters due to the danger of pollution to the drinking water of Glasgow. Instead a wood-burning, steam-powered boat named the SS Sir Walter Scott offers local tourist transport.

All ships in the UK must record a measured mile for sea-worthiness. This ship was built in Denny's ship-yard in Dumbarton and measured its mile in the Firth of Clyde with all normally riveted joints made with bolts. It was then transported by sea, then disassembled and carried on by horse-cart to Loch Katrine where it was re-assembled using rivets.

Fly and boat fishing for trout is permitted on the loch from spring to autumn.