The Bay of Mont-Saint-Michel, one of France’s most iconic and photographed landscapes, has been shaped by a complex history of human engineering and natural processes. For centuries, the area has been a dynamic interplay between the sea and the land, but this balance has been disrupted by large-scale land reclamation projects. In 1856, under the Second Empire, the French government granted a Dutch company a concession to transform thousands of hectares of marshland into arable land. This project aimed to replicate the Dutch "polder" system, which involves building dikes and canals to drain wetlands and create usable farmland. Initially covering between 2,800 and 3,800 hectares, the project expanded further by 221 hectares in 1860, marking the beginning of a significant transformation of the landscape. One of the key consequences of this land reclamation was the canalization of the Couesnon River, which had previously played a vital role in naturally cleansing the bay. By altering the river's natural flow, sediment began to accumulate more heavily in the area. This problem was compounded in the late 19th century when a road dyke was constructed to connect Mont-Saint-Michel to the mainland. This structure disrupted the natural water circulation around the island, leading to the gradual transformation of the once-dynamic maritime environment into a larger expanse of marshes and salt meadows. By 1933, the polders—land reclaimed from the sea—had expanded to cover 15,000 hectares, with some areas extending as close as one kilometer from Mont-Saint-Michel itself. Another major intervention came in 1966, when a dam was built at the mouth of the Couesnon River to prevent flooding. However, this dam inadvertently worsened the siltation problem by blocking the natural flow of sediments to the open sea. As a result, Mont-Saint-Michel became increasingly surrounded by permanent marshes, threatening its status as an island and altering the natural character of the bay. In response to these environmental changes, French authorities launched a restoration program in the 2000s aimed at restoring the bay’s maritime features. This included replacing the road dyke with a bridge supported by piles, which allows water to flow freely and reduce sediment buildup. Additionally, a study program on the polders and marshes of the bay was launched for the period 2022-2026, emphasizing the ongoing importance of managing this delicate ecosystem. Despite these efforts, the challenge of controlling siltation remains, highlighting the difficulty of predicting the long-term impacts of human interventions on coastal environments.