Tameside Time Team anyone?

I often take the hound walking on the banks of The River Tame and when the water level is low you can walk on the sand and pebbles. For mile after mile you find bits of broken pottery of various kinds. At first I thought it was localised to a spot in Haughton Green woods but this is not the case because these fragments of pottery can be found at least as far as Stockport. I had a theory that maybe there was once a ceramics factory on the banks of the Tame and the broken or imperfect pieces were thrown into the river - the only problem with this theory is - I cannot find any reference to such a factory ever existing on the banks of the Tame. Another possibility may be that at one time the river was used as a dump and everything eventually got washed away with the exception of the ceramics which can still be found. Has anyone got any ideas on how these pieces come to be in the river Tame? The photos are of typical items you will find all along the banks of the river. They must have been there for many years because in a lot of cases erosion has smoothed the surface of the fragments.