Leadfingers is more or less right, though there are a tiny handful of traditional ones. You can safely say that ALL songs of the "We were going up the Tardebigge ninety seven, me brave boys, carrying a load of snuff" variety were composed recently by canal enthusiasts.
I would go into this in more detail, but I'm off to rig bunting and fireworks and play music for a series of canal events in Walsall.
   I'll just throw in the name Emma Vickers from Burscough, if we are talking about actual authentic traditional boat songs by actual traditional boat people.