More than a thousand people on 250 boats of all shapes and sizes will be carried up the river.
The flotilla, which has been organised by the Royal Yachting Association, set off from Greenock at around 10am.
It will feature all kinds of boat, from small ships, clipper boats and leisure yachts to working boats.
The boats will sail to Pacific Quay at the heart of the city, where they are expected to arrive at around 1pm.
A viewing area for spectators has been set up at the Riverside Museum on the banks of the Clyde.
The flotilla is part of the Glasgow 2014 cultural programme, a series of events running until the end of August to celebrate the Glasgow 2014 Games.