Is a harbor needed to move supply via river

[charlesonmission]

Does anyone know if a harbor is the only way to move supplies via river or the ocean.

I'm wondering if there is any point in blockading an area without a harbor? Edit (I found out that there must be a harbor to have the blockade option, but the question above still stands)

Second question is this. If I have a fort that has a harbor, and the fort is under siege where I control 5% and the Union controls 95%, is the Union receiving supplies through that harbor?

Charles

[Fingolfin]

From my understanding and experience, the answer is "no" in both cases