The River Calder starts in Cliviger close to Burnley. Its source is very close to that of the West Yorkshire river with the same name, and that of the River Irwell. This part of the catchment used to be important for quarrying and coal mining. Mining waste continues to pollute the headwaters, along with pollution from contaminated land run-off from agricultural activities and sewage discharges. The Calder then flows through Towneley Park before entering the industrial town of Burnley. The Calder is a post-industrialised river and modifications to the physical habitat, including retaining walls, weirs and culverts, is one of the main challenges facing this area. Maintenance of these man-made channels to manage the risk of flooding in the area, including protecting major transport links (road and rail) and the Leeds-Liverpool canal, restricts the development of in river and marginal habitat works in urban areas.