The River Wey (20 miles of towpath at 16x walking speed) 

the River Wey is about 87 miles long and comes from 2 sources, Farringdon in Hampshire and Black down in West Sussex, the river then merges in Tilford Surrey.
The River Wey then becomes navigational from Godalming which was opened in1764. The original part of the navigation was opened in 1653.
This video is the 20 miles of towpath running along side the river from Godalming to the Thames Lock, not far from where the River Wey runs into The Thames.