Today, the production of hydroelectricity on the Amazon region is a high stakes endeavor, associated with negative consequences to environment and local communities, be they Amerindian, peasant, traditional or otherwise. Regardless of strong opposition, Brazilian government continues to envision the countries’ electricity expansion in this direction. This article questions the long history of the relationship between the Brazilian State and Amazonian rivers, focusing on the Tocantins. Through the different uses and representations around the Tocantins River by various actors, at various scales and over the long term, it aims at understanding how, from a means of access, transport, exchange and communication, this river is transformed into a hydroelectric potential and therefore a resource. By examining the ideas and demands around river development by local elites and the central State, from the colonial era to the Twentieth century, it deals with the evolution of the role of rivers in policies aimed at regional development. In this analysis the role of water as an essential element to understand politics in the Amazon emerges. Furthermore, the article shows the importance of politics at the local scale on the evolution in the relation between claims and priorities in river development policies.