It would not have occurred to me that the landlocked Idaho has access to the sea for oceanic transport, but it does. The Snake River touches the Port of Lewiston on the western border of the state. That river connects to the Columbia River and thence the Pacific Ocean.
The US Department of Transportation refers to this route as Maritime Highway M-84. Note that this route does not provide sea access for the US Navy's submarine base in Idaho.
I should mention that Lewiston is not the most inland port of the United States. That would be Duluth, which can dock oceangoing vessels traveling along the Great Lakes and the St. Lawrence Seaway.
-via Battle Beagle
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