This article examines the effects of recognising the rights of the Mar Menor by questioning the traditional concept of efficacy. Having become the first European natural entity to be recognised as a legal entity in 2022, the Spanish lagoon of Mar Menor would seem to be an ideal case study for empirically assessing the efficacy of Rights of Nature in Europe. However, field research suggests that the rights of the Mar Menor have effects that go beyond legal efficacy. Drawing on the concept of creolisation theorised by Édouard Glissant, I propose to describe the rights of the Mar Menor as a European creolisation of the rights of nature. I then develop the concept of fecundity to describe the political inventiveness of a law that invites the creation of new institutions for political deliberation on the future of the living community.