Water is life. For millennia, the Rio Grande/Rio Bravo has nourished many Indigenous peoples along its 1,255 mile length, from it's source in the San Juan Mountains to the Gulf of Mexico. The river is the lifeline, read as a map between the interrelated communities. Colonization turned the Rio Grande/Rio Bravo into an international border between the United States and Mexico, and in the last 40 years, our river/border has become heavily militarized. This project engages a practice of Indigenizing/decolonizing the Rio Grande/Rio Bravo as ancestral waters to various local Indigenous peoples, drawing from the collective memory of intergenerational indigenous fronterizxs (border residents) to examine the relationships between people of the Laredo/Nuevo Laredo community and the Rio Grande/Rio Bravo. To do this, I theorized a new theoretical framework called an Indigenous Fronterizx Cosmography, which braids Indigenous epistemologies, Xincanx ontologies, and borderland positionalities. This way, first-hand accounts are understood as intellectual traditions that revitalize, restore, and restory the holistic ancestral knowledges of the land and river. Next, I created a culturally-centric research methodology, named Fronterawork, drawing from Indigenous methodologies, oral history/testimonio sharing, and witnessing to document the lived experiences of 25 community elders and knowledge-keepers in/of/with/near/over/across the river's waters. Participants shared their knowledge of the Rio Grande/Rio Bravo, as well as their perspectives of how the river has changed over their lifetimes. Their testimonios were examined holistically, and in-context as embodied and emplaced situated knowledges of the river. When considered in conversation with each other, themes and subthemes emerged, suggesting two major approaches to understanding: river-as-water (Water Thinking) and river-as-border (Border Thinking). In response, I created a Pedagogy of Water that builds on the collective memory of community elders in order to teach the next generations about our river. This pedagogy interrupts dominant forms of displacement and violence against the diverse Indigenous peoples of the river/border communities, while revitalizing the ancestral relationships between the Indigenous peoples and the Rio Grande/Rio Bravo. Our collective memory serves as foundation from which to revitalize and honor the Rio Grande/Rio Bravo as part of the sacred landscape of what is today called south Texas.