Locals say they have "grave concerns" over rising water levels at the Ffos-y-Fran opencast site
BBC. Merthyr Tydfil's Ffos-y-Fran mine was responsible for 86% of the UK's total coal output before it closed.
Residents who live near the UK's largest opencast mine have "Grave concerns" over rising water levels at the site.
Work at Ffos-y-Fran stopped in November 2023, and emails shared with BBC Wales show Merthyr Tydfil council believes a revised restoration proposal will include a body of water.
The mine's operator - Merthyr Limited - said ground water levels were being continually monitored as it worked on updated plans for the site's restoration.
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The council said there were currently no plans for the mine's operator to "Reintroduce pumps on site to remove the water from the mining void".
Ffos-y-Fran is officially classed as a "Land reclamation scheme", meaning the vast site close to homes and businesses in Merthyr Tydfil was to be restored to green hillside for the community's benefit.
A spokesman for Merthyr Limited said ground water levels had been monitored on a regular basis since mining had stopped in November, "Under the guidance of a consultant hydrogeologist".
"Following one of the wettest winters on record ground water levels have stabilised around the levels monitored prior to commencing mining operations," he said.
Merthyr Tydfil council said it continued to work with the company "To agree interim restoration works prior to the submission of a future revised restoration strategy".