In 1714, the people of Bern, a canton in modern-day Switzerland, redirected the Kander River into Lake Thoune by digging a tunnel through the Strättligen hill. This engineering effort caused the riverbed to drop sharply—about 27 meters at its deepest point within two years, according to historical records. Other measurements showed smaller drops of 21 meters and 5 meters, indicating that while the changes were dramatic, they were not uniform across the entire riverbed. The tunnel eventually collapsed, giving rise to the Kanderschlucht, a deep gorge that now lies in its place. Before the 1714 project, the Kander River flowed along Lake Thoune and the city of Thun before joining the Aar River. Over time, the river’s sediments narrowed the Aar’s channel, leading to frequent flooding in Thun. Samuel Bodmer, a local engineer, proposed diverting the Kander into Lake Thoune to absorb the sediments. The project, approved in 1711, involved digging a trench and then a tunnel through the Strättligen hill so the river could flow into the lake near Gwatt. Today, the Bernese government calls the 1714 project "audacious and visionary," noting that it dramatically altered the Kander's course. However, the builders assumed the tunnel would remain stable, but the river quickly eroded it, leading to the formation of the Kanderschlucht through a process known as regressive erosion. This occurs when a river suddenly drops to a lower level, such as a lake, and begins to erode its bed at the point of the drop, gradually moving upstream. According to a model from the University of Bern, the river eroded nearly a kilometer of valley in 12 years, creating a significant delta of gravel in the lake, exactly what Bodmer had intended. However, the speed of the erosion was unexpected. The historical data comes from observations made by Koch in 1826 and later cited by the University of Bern. These show that the riverbed dropped by as much as 27 meters in two years at one point, with smaller drops recorded at other locations. More recent studies, including a 2017 poster presented at the EGU, suggest a drop of 30 meters over four years, aligning with the model’s estimate of 29 meters over the same period. Today, the Kander flows through a gorge about 80 meters deep before reaching Lake Thoune, a figure that reflects the current state of the landscape, not the initial rapid erosion. Despite the project’s success in diverting sediments, it had unintended consequences for Thun. The city, which the project aimed to protect from flooding, instead faced increased water flow and material from the Kander, while the Aar River’s outlet remained unchanged. This led to repeated flooding and required extensive modifications to the river’s course and infrastructure over the following centuries. Today, the 1714 diversion still influences the hydrology of Lake Thoune and Thun. The Kanderschlucht, however, remains a dynamic natural feature, with ongoing efforts to maintain structures like the Strättligsteg bridge near Gwatt, which is expected to undergo restoration by 2026.