What major body of water borders New Mexico to the south?

New Mexico is bordered to the south by the Rio Grande, which serves as a significant natural landmark and water source for the region. The Rio Grande is one of the longest rivers in North America, flowing from Colorado, through New Mexico, and forming a part of the border between the United States and Mexico. It plays a crucial role in the geography, ecology, and agricultural practices of New Mexico, providing essential irrigation for farming and supporting a variety of wildlife along its banks. Additionally, the Rio Grande has historical significance, as it has been a vital resource for Indigenous peoples and later explorers and settlers. This connection to both the landscape and cultural history makes the Rio Grande the correct answer to the question.