In the wake of the COP21 conference in Paris, the transition to a low-carbon energy supply remains a central issue on the political agenda. The deployment of renewable energies is often challenged by multiple issues (e.g., public acceptance, landscape protection, and so forth). Political actors try to overcome such challenges with various measures; however, the policy instruments used vary greatly in their strength. This article questions what factors lead to the adoption of strong policy instruments promoting hydroelectricity. Explanatory factors are derived from Kingdon's multiple streams framework and are analyzed with fuzzy-set qualitative comparative analysis within the Swiss cantons. The findings show that the strength of policy promoting hydroelectricity depends on the conjunction of mainly two factors: ambitious climate targets and an already well-established hydroelectricity sector that generates large tax revenues for the cantons. Depending on the context, the strength of left-wing and green parties as well as the current level of exploitation play an important role with the aforementioned factors.