The River Medlock is carried through many culverts on it's course to the Irwell. Downstream near the city the underground passage of the river has been documented pretty well, but I could find nothing from further upstream. Up near Oldham and it's source the Medlock is a small river and as such requires small culverts, so I was surprised to find quite a reasonably sized one.
I walked in from the outfall and found a large brick arch, the sides were scattered with stone debris with the river flowing sedately inbetween. The culvert has an industrial feel with pipes protruding and metal bars holding bits of it together. A business still exists above to which the river may owe it's original reason for being covered over. At a few points light enters through grilles above and you can get a suggestion of what is above.
The culvert is about 160m long, towards the infall things started to get interesting. A small step allowed the stone and metalwork that comprised the floor to be seen. A series of metal sheets hid a number of small side passages, the largest could easily be stooped. Looking down this a low brick chamber could be seen with a trickle of water coming from a further small tunnel.
I started taking photos and no sooner had I got the first of a lovely water slide, I saw some people poking round the infall. Not knowing their intent and being by myself I slid off back to the outfall grabbing the few pics along the way.