The River Croal in bolton is a tributory of the river irwell where it meets at "nob end". It flows beneath the centre of Bolton town below knowsley street, Market place and Birdge street.
Most of the river is culverted but there is a mixture of open and underground channels throughout its span.
The culvert is a nice contrast of concrete box, brick and stone work.
Before 1836 the River Croal was the boundary between the townships of great and little Bolton.
Currently seems to be the goto place for the local crack heads.