Abstract: The paper delves into the process of refurbishment of an old metal bridge (year 1905) located in a marsh (mouth of the Ason river, Cantabria) of high environmental value. The repair was necessary to guarantee the structural safety of the bridge, which serves a national road (N-634). At the same time, it was necessary to preserve its cultural values and, during the work, to fulfill the environmental requirements. The text emphasizes the importance of having a good record of information on the bridge in order to plan a good intervention. The results confirm that the previous studies have been useful to project and execute a deep repair, respecting the cultural landscape of the estuary.