From vDip:
"Waterways - There are two waterways in Empire4 where fleets can move as though there were a coastline in the listed territories. These rivers do not impede army movement:
Mississippi (Chicago, Missouri, Kentucky, Tennessee, Arkansas, Deep South, Louisiana)
St-Lawrence (Beauce, Montreal, NYS, Ontario, Quebec, Gaspe)
For example, a fleet could move from Tennessee to any of Kentucky, Missouri, Arkansas or Deep South"
See http://vdiplomacy.com/variants.php?variantID=20