^ Switzerland lacks a seaport and yet it has one of the highest per capita GDPs on the planet.
Also, thanks to the great lakes and the mississipi-ohio-missouri river waterway systems, the only states that truly lack navigable waterways to the ocean are those of the interior mountain west - ID, MT, NV, UT, WY, CO, AZ & NM.
Navigable waterways and interior port cities of the US
Source: wikipedia