The thing that has changed fish stocks in the canal system is boats, When i was a kid the canals were pretty run down, Eroded tow paths that were impassable in places, Weed covered both the near and far margins, However they were dredged regularly usually by means of a sludge pump that would spray the silt onto bordering fields, Tench were seen rolling after spawning in the weeds and i mean a lot of them. The water was very clear. you could watch the shoals of perch from off the top of bridges. Then It started to change, Boating got more popular. The tow paths were improved and more moorings a