Number of existing infrastructure assets of the waterway infrastructure portfolio, built prior to the1900s is still in use today. While these infrastructures have already exceeded their expected service lifetime of 100 years, they are exhibiting complex deterioration mechanisms that do not only impair their structural reliability as well as availability, but also pose substantial threats to the social and economic growth of Germany. In response to ongoing degradation processes, associated to combined effects of aggressive environmental stressors, operating conditions and deferred maintenance, a Maintenance Management System (EMS-WSV) has been set up from 2008 by the Federal Waterways Engineering and Research Institute (BAW). Condition grades developed within the EMS-WSV serve for decision making regarding maintenance interventions. However, these condition grades do not sufficiently address the effects of deterioration mechanisms on the structural reliability of waterway infrastructure assets and the emerging risk of infrastructure failure is not also taken into account. The aim of the present paper is to use a very simple approach, namely the Fuzzy Failure Mode and Effects Analysis (Fuzzy-FMEA), to derive additional key figures, taking into account the aforementioned shortcomings. The proposed approach is implemented in this research to rank seven navigation locks of the Main-Danube-Canal (MDK) for maintenance interventions. Due to the complexity of their structural design, reinforced concrete infrastructures pose the most serious risks of infrastructure failure. Thus, fatigue induced-damage, corrosion of the steel reinforcements and inaccuracies in load assumptions are identified as main causes of failure that may hinder the load carrying capacity of these structures.