A stretch of railway near Llanelli has reopened six months after a train derailed in a major incident that saw homes evacuated and sparking huge environmental concerns.
The freight train derailed while travelling through the village of Llangennech in August, causing it to catch fire before spilling around 350,000 litres of diesel.
A major incident was declared and homes were evacuated, with around 300 people affected.
Two train workers escaped unhurt.
The incident - which occurred close to the Loughor Estuary - caused major concerns for the surrounding wildlife conservation area and waterways.
It led to one of the biggest environmental recovery efforts Network Rail has ever been involved with.
The southern end of the Heart of Wales line, which runs from Shrewsbury to Swansea, has been closed ever since.
Ground teams have spent a total of 37,500 hours working to protect the local environment, remove the wagons and repair the damaged railway.
Natural Resources Wales, who compared the scale of the incident to the Sea Empress disaster of 1996, will continue to monitor the shellfish and wider environment over the coming months.
30,000 tonnes of contaminated soil have been excavated from 150 metres of railway, at a depth of two metres and width of 20 metres.
That soil has been replaced with new, clean material from quarries in Carmarthenshire and Pembrokeshire, with the fuel-soaked soil taken to a licensed waste management facility in Merthyr.
In the final few weeks of the recovery, Network Rail worked to fit around 530 metres of brand-new track before reinstalling the signalling, which was damaged by the fire.
Freight services started back on the railway line through Llangennech on Friday.
Bill Kelly, Network Rail Wales route director, said: "It is thanks to our quick-thinking frontline teams, along with our partner agencies, that the fuel spill was able to be contained so swiftly, allowing us to prevent what could have been a total environmental disaster.
"Our teams have worked non-stop for the past six months and their dedication has paid off.
"We can confidently say the measures we have taken will protect the local environment for generations to come."