What was the way that Lewis and Clark expedition failed?

The expedition's goal as stated by President Jefferson was "to explore the Missouri River, & such principal stream of it as, by its course & communication with the water of the Pacific ocean may offer the most direct & practicable water communication across this continent, for the purposes of commerce." In addition, the expedition was to learn more about the Northwest's Natural Resources, inhabitants, and possibilities for settlement. In the end, they were able to find and categorize 122 new animals and 178 plants, mapped the geography, and achieved friendlier relations with the natives. However, they did not find an all water route to the Pacific Ocean.