Anguillid eels are under pressure from multiple threats, such as; habitat loss and modification; overexploitation; illegal, unreported and unregulated fishing; migration barriers; pollution; disease; parasites; and climate change, and many species are declining in number. There is therefore an increasing need for evidence-based conservation of anguillid eel populations. Reviewing the evidence is a time-consuming and costly exercise. In general, the assessment of the evidence-base is approached on a case-by-case basis and different stakeholders independently conduct evidence reviews relative to their specific application or enquiry. This approach is counter to the philosophy of ‘produce once and use many times over’ and is a highly inefficient use of resources. The methods outlined in this protocol are designed to identify and synthesise the available evidence for the effectiveness of conservation interventions for anguillid eels that are carried out in freshwater habitats. This protocol uses wording that is standard for a subject-wide Conservation Evidence synthesis.