2.3.4 (RYEW) Can navigate through some rivers, but not the others

[Gomissar]

Long story short, my character is reformed Norse and I can't sail through Seine, other French rivers, first three sections of Danube, first section of Rhine. Other rivers work fine. I discovered this bug during a war with France, so I don't actually know when it showed up.
Couldn't reproduce this bug in a new game. I also can't upload my save due to "There was a problem uploading your file" error.

 

[Dracko81]

You can't navigate rivers which have had fort levels increased.

 

[Gomissar]

I see. A tooltip would be useful, though, since it still shows green arrow when I target those rivers.

 

[Yxklyx]

You can't navigate rivers which have had fort levels increased.

What level of fort?

 

[Dracko81]

What level of fort?

MAX_RIVER_MOVEMENT_FORT_LEVEL = 10.0,

From the defines.

 

[Servancour]

As Dracko mentions, the level of Fort Level present determines if you are able to navigate the river or not. However, it's not as straight forward as having a holding with 10 Fort Level present. Looking at the code, it seems like it currently calculates an average for all neighboring provinces, and that average cannot be more than 10 for you to navigate it.

I'll file an improvement in our bug database for actually adding this information to the game somehow and make it more clear as to why you may, or may not, navigate a river.