Hughes composed the poem while crossing the Mississippi River on his way to visit his father in Mexico when he was seventeen. It was initially published in The Crisis the next year, establishing Hughes' literary career. The poem is often considered one of the first examples of modern poetry. The reference is to the Mississippi River. Before the river was bridged, it was possible to travel from New Orleans to St. Louis by boat. Crossing the river was not easy, because the water was frequently too deep or rapids were present. But for those who could do it, the experience was well worth it. The poet himself had good reasons to appreciate the beauty of the river. His family lived in Louisiana and Missouri, two states that were then part of the United States. Perhaps this is why Hughes chose to cross the river when he was going to see them anyway. In addition to being a famous author, Hughes was also black. This fact may explain why some people think that the poem is about slavery. But it's not really about slavery per se, it's about freedom and self-determination. Even though slavery once existed on both sides of the river, it was ending in the South but still existed in the North. That's why Hughes can say that the river is "great" even if most people at the time didn't feel free to go wherever they wanted.