Around 330 crews take part in the 22 mile race from Docklands to Ham.
Traditional boats, or traditional-style replicas, powered by a minimum of four oars or paddles may enter.
From 9.50am boats leave Millwall drawback on a 'slowest first, fastest last' handicap basis, giving all crews an equal chance.
The first boats reach Tower Bridge about 10.20am and Lambeth Bridge about 20 minutes later.
Related website: www.greatriverrace.co.uk