To promote the sustainable management of hydropower, decision makers require information about cost trade-offs between the restoration of fish passage and hydropower production. We provide a systematic overview of the construction, operational, monitoring, and power loss costs associated with upstream and downstream fish passage measures in the European context. When comparing the total costs of upstream measures across different electricity price scenarios, nature-like solutions (67–88 EUR/kW) tend to cost less than technical solutions (201–287 EUR/kW) on average. Furthermore, nature-like fish passes incur fewer power losses and provide habitat in addition to facilitating fish passage, which presents a strong argument for supporting their development. When evaluating different cost categories of fish passage measures across different electricity price scenarios, construction (45–87%) accounts for the largest share compared to operation (0–1.2%) and power losses (11–54%). However, under a high electricity price scenario, power losses exceed construction costs for technical fish passes. Finally, there tends to be limited information on operational, power loss, and monitoring costs associated with passage measures. Thus, we recommend that policy makers standardize monitoring and reporting of hydraulic, structural, and biological parameters as well as costs in a more detailed manner.

Increasing awareness of the complexity of river ecosystems has led to the emergence of integrative disciplines that combine topics in river physical and ecological processes, exemplified by the disciplines of ecohydrology, hydroecology and ecohydraulics. However, the names of these disciplines are often referred to interchangeably without attention paid to their meaning. This ambiguity impairs the efficient development and widespread promotion of these fields of study and their applications. To address this issue, we strive to clarify the definitions and contributions of the different disciplines. This is done by exploring their interrelationships and providing a reference for the integration of disciplines in these evolving fields. Finally, we advocate for ecohydrology and ecohydraulics to be considered complementary, and not duplicative, disciplines within river science. We further argue that awareness of their similarities and differences is important to address key issues in river science and to ensure ecohydraulics finds its positioning with respect to other disciplines, as well as current and emerging societal and scientific challenges, such as climate change.