The major river that runs through Brazil, known for its biodiversity, is the Amazon River. It is the second longest river in the world and flows across several countries but primarily through Brazil, where it serves as a vital waterway. The Amazon River basin is home to an unparalleled variety of flora and fauna, making it one of the most biodiverse regions on the planet. The river system supports countless species, indigenous communities, and ecosystems, playing a crucial role in both local and global environmental health.