Abstract: My dissertation examines how Brazilian modern water resources management in the Sao Francisco River has obtained its authority through a set of discursive displacements rooted in late 19th century imperial and early 20th century republican visions of nature and race. I argue that those discursive displacements, especially along the São Francisco River banks and islands, construct and give meaning to one entity---the 'river of national unity'---within a historically and geographically specific system of signification (transportation, electric energy, irrigation, crops, and productivity) that is genealogically related to geopolitical aspirations supported by 19th century scientific and engineering river expeditions. The São Francisco River extends through six Brazilian states, crossing semi-humid and semi-arid terrains as it moves from the central-south highlands of Brazil to the dry northeast plateaus and mesas. The river drains water from an area of 644,000 km2, 8% of the Brazilian territory, with a current approximate population of 18 million people, living in 503 municipalities, including the capital city of Brazil, Brasilia DF. Based on archival information gathered from government and industry sources, as well as over 60 semi-structured personal interviews and participant observation with artisanal fishing communities, natural scientists, policymakers and social and environmental activists involved with the São Francisco River in the states of Alagoas, Bahia, Pernambuco, Minas Gerais, Sergipe, and Goias, this study points to historical, cultural and political processes through which the identities living in, working on and managing the São Francisco River attain legimaticy. This study argues that representations of the São Francisco River have evolved from the modernizing 'river of national unity' to a 'landscape of mourning' evoking the return of traditional cultural values. In that sense, my story unfolds the national discourse of modernization of the São Francisco River as the backdrop to the displacements it carries to the ecology and the 'traditional way of living' along this River. My findings show that developers during the mid 20th century made the traditional communities along the river invisible on maps and plans. This enabled the large water projects to 'work' in controlling nature and stabilizing social and political movements, while erasing 'traditional' cultures from national views. However, since the mid 1980s, protests along the São Francisco River against large water projects led initially by priests of the Catholic Church, and then by NGOs and civil society, invoked traditions along the river---for instance portrayed by gendered and racial images of traditional artisanal fishermen---as a call for river preservation. Although the images of traditional fishermen represented the river as their place of livelihood, their very localness has nonetheless challenged the hegemonic representation of the São Francisco River as 'the river of national unity', based on the assumption that the river has to support large infrastructure projects, into one of 'disunity', based on the assertion of local identity claims. (Abstract shortened by UMI.)