Major hydraulic projects have a long tradition in Spain and must be contextualised within the framework of the so-called “hydraulic paradigm”, according to which demand must be met with a sustained increase in supply. These large projects, which include but are not limited to the construction of large reservoirs, share a series of characteristics: their implementation relies on state economic and ideological support, their socioeconomic impact tends to be overestimated, their cost tends to be underestimated, they are presented as politically neutral, and they are the source of socio-environmental conflict. In order to gain a better understanding of this, we analyse the conflict generated by the dredging of the Guadalquivir River (Proyecto de Mejora de Accesos Marítimos al Puerto de Sevilla—MAM), a project aimed at improving navigability and access to the harbour of Seville (Spain). This project has highlighted the tensions underlying decision-making processes which pitch hegemonic policy makers against the rest of the stakeholders, as well as the lack of integrative and adaptive perspectives, institutional transparency and effective participation of all stakeholders in hydraulic policies.