This article explores the trade-offs in the decarbonisation of the energy sector by analysing the legal arguments in favour of and against hydropower in EU law. It contends that the EU regimes in climate, energy and environmental law each value the advantages and disadvantages of energy production in different ways. In contrasting the approaches in these three areas of EU law, the article analyses how EU law governs the decarbonisation process in the context of hydropower. The analysis reveals a promising opportunity to reconcile the friction among climate, energy and environmental law while improving the ecological sustainability of hydropower production.