Beneath the town of Moutiers in Meurthe-et-Moselle, a large body of water has been accumulating in abandoned underground mining tunnels since the mid-1990s. This water is not the result of recent mining activity or explosions, but rather the consequence of a long-forgotten pumping system, known as the "exhaure," which once kept the tunnels dry. When the last iron mines in the region closed between the late 1980s and mid-1990s, the pumping system was gradually shut down due to economic reasons. Without this system, water began to fill the empty tunnels, leading to unexpected consequences. The Lorraine iron basin, which spans from Longwy to Nancy through Briey and Moyeuvre-Grande, was once a hub of iron ore extraction, with generations of miners carving out a complex network of tunnels and chambers. These tunnels were supported by pillars of rock, and the exhaure system ensured they remained dry while mining was active. When the system stopped, water seeped into the tunnels, coming into contact with rocks and mining waste. This interaction caused sulfates to dissolve into the groundwater, affecting the quality of drinking water in several communities in the area. In response, water resource services have had to adapt their monitoring techniques, adding more control points and adjusting their methods to ensure the water remains safe for consumption. On the surface, the presence of water in these underground voids has changed the pressure on the rock pillars and tunnel ceilings, leading to ground subsidence in some areas. In Moutiers, a significant subsidence in 1996 forced the evacuation of homes that were at risk, an event that has left a lasting mark on the region’s collective memory. To prevent future incidents, authorities have installed monitoring devices, motion sensors, and conduct regular topographic surveys in areas considered fragile. Many communities in the iron basin have also developed risk prevention plans, limiting or strictly regulating new construction above old mining sites to reduce the chance of damage. Despite the mines closing 30 to 40 years ago, the effects of the underground flooding are still being felt today. The water continues to move slowly through previously unexplored tunnels, and the underground landscape is still adjusting. Regional geological services are constantly updating risk maps as new sensitive areas are discovered. A century of mining has left a visible mark on the landscape, but its impact continues to shape the underground environment, reminding us that the consequences of past industrial activity can persist for decades.