On the night of 26 August 2020, a freight train carrying over two million litres of diesel derailed, spilling over 300,000 litres into a highly sensitive environment. The impacts from this once-in-a-generation incident are now largely fully recovered, in an operation described by the environmental regulator in Wales as amongst the most challenging in the last 25 years. The presentation will share an overview of that operation, including the emergency response efforts and the strategy developed to successfully deliver the ongoing containment, investigation, assessment, and restoration of the spill.