In 1817, the Rhine River flowed freely between the cities of Basel and Lauterbourg, winding through a landscape of meanders, oxbow lakes, and shifting islands. This natural flow, while beautiful, was unpredictable and dangerous. Floods frequently damaged nearby villages, destroyed crops, and spread diseases like malaria through stagnant water. To address these issues, Johann Gottfried Tulla, a Baden engineer, proposed a bold plan: to straighten the river’s course to make it more navigable and reduce flooding. This ambitious project, which lasted over sixty years, would dramatically alter the landscape and have lasting environmental consequences. Tulla’s work between 1817 and 1878 reduced the Rhine’s length between Basel and Lauterbourg from 262 to 180 kilometers, effectively removing nearly 100 kilometers of river from the map. By straightening the course, the river’s current became faster, and its bed deepened by 5 to 10 meters in some areas. This change had an unexpected effect: it lowered the groundwater level in the surrounding region, cutting off the old river branches and the wetlands of the Ried from their water supply. Although the project succeeded in reducing floods and improving navigation, it also set in motion a slow but significant decline in the region’s groundwater levels, a problem that persists to this day. The Rhine’s transformation into a straight, fast-flowing river had profound ecological effects. The deepening of the riverbed caused the surrounding groundwater to flow downward, lowering the water table across the Alsace plain. This invisible change had far-reaching consequences. The old river channels, now elevated above the new water level, could no longer be flooded, leading to the drying out of wetlands and the loss of habitat for fish and other wildlife. The alluvial forests of the Ried, which relied on the rising groundwater to sustain their roots, began to wither. Despite being in close proximity to the Rhine, these forests now suffer from chronic water shortages, a result of the engineering project that reshaped the river over a century and a half ago. In the 20th century, further modifications, such as the construction of the Alsace Grand Canal, continued to lower the groundwater level, prompting the installation of the Breisach dam to artificially maintain water levels. Today, the Rhine’s groundwater remains the largest underground water reserve in Western Europe, supplying millions of people across France, Germany, and Switzerland. However, recent drought alerts have highlighted the vulnerability of this system. In response, the Ill-Groundwater-Rhine SAGE, covering 322 communes and nearly 3,600 square kilometers, is working to restore groundwater levels and revive the wetlands and rivers damaged by past engineering efforts. Two centuries after Tulla’s project began, Alsace faces the challenge of managing a river that has been tamed but at a cost. While the region benefits from flood protection and improved navigation, the forests and wetlands now require careful rehydration to recover. The history of the Rhine serves as a reminder that altering a river’s course can have long-term, often unseen, consequences on the environment. As efforts continue to restore the region’s groundwater and ecosystems, the question remains whether these efforts will be enough to bring back the water that was lost more than a century ago.