The original Erie Canal and the present Barge Canal had paths on each side, called towpaths, that allowed draft animals to pull canal boats in the years prior to motorized shipping. Once the boats no longer required external power, the paths fell out of use (although the right-of-way remained). Some sections remained in use, however, particularly the part between Genesee Valley Park and Pittsford which was actually paved with blacktop. In the 1980's the paving was extended further east to Fairport and west to Gates and beyond.
Traveling west from Fairport, the paved section is on the north side of the canal. At Genesee Valley Park the paved section switches to the south side of the canal. There is still a path on the unpaved sides but the land may not be accessible due to homeowners' landscaping or docks. The South side between East Henrietta Road and Edgewood Avenue is in good condition and not encumbered by landscaping. It's a frequent destination of dog walkers, so be careful. It is paved with cinders, not blacktop.
The path is multiuse, so you will encounter walkers, runners, baby strollers, rollerskaters, cyclists and who knows what else. It's always a good idea to pay attention. In the summer of 2005 the path in the Brighton area had a single white line painted down the center to separate Eastbound and Westbound traffic.
Because the canal travels under a number of heavily-used roads, you will be faced with road crossings in some places. Stairs are available at Clover Street and Edgewood Avenue (dismount your bike first) and traffic lights in a few others. Otherwise, look both ways and cross carefully.