Why was the Missouri River important to the Lewis and Clark expedition? The river could be followed by their wagon train, so their horses would have a source of freshwater. The river could be followed by their wagon train, so their horses would have a source of freshwater. , , The river allowed the expedition to travel easily through the territory with their equipment. The river allowed the expedition to travel easily through the territory with their equipment. , , The river was used by American Indians and would provide access to trade along the way. The river was used by American Indians and would provide access to trade along the way. , , The river was famed for its abundance of fish, so they knew the expedition would have enough to eat.