In March 1988 opencast coal mining at the St Aidans extension site near Leeds was brought abruptly to a halt by a catastrophic failure of the 70 m deep excavation wall and the resulting inundation by the River Aire. This paper describes the planning, design, construction and recovery of the site, which involved the construction of the first significant new section of canal in the UK for over 90 years, Environmental considerations were a major factor at all stages of the design and construction. In order to separate the opencast void from the river a new 3.5 km long watercourse combining the river and the canal was constructed. The route was constrained by the stability of the excavated void slopes and was located in a narrow corridor between the existing canal, a railway line and several lakes, through a disused colliery, a coal mine tip and an abandoned unlined waste disposal site. Construction of the watercourse involved the excavation of 3.5 million m(3) of variable material under extensive dewatering operations and lining with compacted mudstone and riprap stone protection. The works were successfully completed in early 1995.