SK3181 : A rusty springThis is actually on the location of an old mine shaft, part of the old Dore Colliery workings. The shaft is very shallow - less than 10 m as I recall, and almost certainly was used to drain the mine workings which were all located up-dip from here.
The ochrous discharge has been running for at least 80 years and almost certainly longer than that, as the Dore colliery workings were abandoned in the latter part of the 19th century.
I was involved in a scoping study to investigate the feasibility of cleaning or halting the discharge, but the conclusion was that the environmental impact of a treatment works - clearing woodland and creating reed beds to filter the water, etc. - would be far more serious than just leaving the discharge to run as it is.
So the site of the discharge has been fenced off and the water quality is monitered from time to time by the Environment Agency. It's actually not too bad. Also, there is an industrial archaeology interest angle on this, as much of Ecclesall Wooods and the nearby Ryecroft Glen has been the site of former industrial uses: bell pits for coal and ganister, Q-pits for white coal manufacture, lead-smelting boles, etc. Some of these are explained in the information boards dotted around the woodland.