The EU Water Framework Directive (WFD) puts forward ambitious ecological objectives on reaching good status in surface waters throughout the EU. In rivers harnessed for hydropower production, achieving these aims would in many cases necessitate requiring new measures to mitigate the operation’s harms to the river ecosystem. Building on the ideas of adaptive management, the Directive requires Member States to establish a system of rules that enables reviewing hydropower authorizations and ensuring that its objectives are reached. However, it is widely recognized that principles of legal certainty and protection of fundamental rights that are part of the rule of law ideal can limit the law’s capacity to mandate such adaptation. This article assesses the interplay between the WFD’s requirements on adaptation and the principles of rule of law in the EU law in relation to review of hydropower permits. The article concludes that while the EU rule of law is itself quite dynamic and amenable to adaptation, respecting the principles of rule of law puts some requirements of clarity, stability and protection of individuals in the EU legislation and its implementation. water framework directive; good ecological status; adaptive law; hydropower; permit review; EU rule of law