In the last twenty years, participatory forums have been increasingly used to manage water basins around the world. The implementation of participatory forums has sought to prevent and overcome conflicts by bringing together a multiplicity of stakeholders in joint efforts to deliberate, achieve mutually agreed upon decisions, and distribute limited water resources. Different literature streams have evaluated the benefits and challenges of participatory forums in practice, such as the difficulties some forums have had when confronting existing power structures. Separately, research on water governance has paid particular attention to the ways in which expert discourses are used by traditionally powerful actors to exclude less powerful others. This paper draws from the literatures on participation and discourses in environmental governance to empirically investigate how expert discourses may empower or disempower certain actors in four basin councils – two in Peru and two in Brazil. Through qualitative thematic analysis of 116 interviews and observation notes, we specifically investigate the extent to which expert discourses in these basin councils help empower previously excluded actors. Our findings indicate stakeholder interests that are not, or cannot, be expressed within the frame of expert discourses are often marginalized. This suggests participation has made it possible for some previously excluded actors to have a voice, yet their potential influence is seemingly confined to a restricted space beyond which their voices will have little effect.