What is the name of the river that the heroes must cross in the Lord of the Rings universe?

In the Lord of the Rings universe, the river that the heroes must cross is called the Anduin. It is also known as the Great River, and it flows from the Misty Mountains to the south of Middle-earth, where it empties into the Bay of Belfalas. The Anduin is an important waterway in Middle-earth, and it plays a significant role in the plot of the Lord of the Rings.

Throughout the story, the Anduin serves as a boundary between different regions of Middle-earth, and the characters must cross it several times during their journey. It is also home to several important locations, such as the Falls of Rauros and the island of Tol Brandir. The Anduin is also the site of several key battles, including the Battle of the Pelennor Fields.