Scotland’s canals are run by a Government body with the does-what-it-says-on-the-tin name of Scottish Canals. All four of them are open for cycling.
Fort William to Inverness. This waterway along the Great Glen joins several lochs, including Loch Ness, with several canal sections. The canal was built with a towpath but the lochs obviously weren’t! For cyclists, the best route is along NCN 78 (the Caledonian Way), which links the gravelly canal towpath with forestry tracks, a converted railway path, and minor roads. It’s not ideal for fast road bikes but fine on anything that can handle a bit of gravel.
Lochgilphead to Crinan. Famously pretty yacht canal that shortens the route to the Hebrides. Fully suitable for cyclists, and part of the long-distance Caledonian Way.
Glasgow–Falkirk and Falkirk–Edinburgh. A continuous towpath cycling route between Scotland’s two greatest cities. In Glasgow, there’s a spur from the main route at Maryhill towards the city centre. Otherwise, you can continue to Port Dundas along the canal, and from there to Dumbarton on a tarmac cycleway. The surface is generally good, often light gravel though occasionally a little muddy: the Union Canal is the more erratic of the two. Signposted throughout as NCN route 754.